The correct answer is C.

First, we need to figure out how to get the correct sequence. We do this by:

1. Find the letter on the keyboard.

2. If the letter is NOT at beginning of the row, then type the letter to the LEFT. If the letter is at the beginning of the row, then type the letter at the end of the row.

3. Repeat these steps for each letter in the word.

This gives the correct answer as:

In option A, the second sequence is not correct: R & T are being used as if there was no keyboard malfunction.

In option B the first sequence is not correct: MW gives us OE instead of the EO in PIGEON

In option D the three sequences are not correct. They apply the opposite rule of the malfunction.

This is Informatics

Concept: Input, Processing, Output devices

When a key is pressed, an electrical circuit is closed and the computer/device receives

a signal about which letter, number or symbol to output to the screen. If there

is an error in the circuit, then it can cause the wrong signal to be sent and the wrong

letter is displayed on the screen. Alternatively, the circuit may not close after a key is pressed which results in no signal being sent, so nothing is displayed on the screen.

Concept: Software Engineering, AI

In other situations, the software is also processing the letters that are input from the keyboard and that is how we can have features like “autocorrect”, which makes corrections to words that are spelled incorrectly. Also we can have “predictive text” where the software can predict what your sentence is going to be and you can complete with a single keystroke.

Question: Could autocorrect or predictive text have helped Luisa?

Concept: Cryptography, Encryption, Decryption

We can draw a parallel of the malfunction with a simple form of encryption known as

a the Ceasar cipher, Shift cipher or Substitution cipher. With the cipher, each letter is replaced by another letter that that is a fixed distance away in the alphabet. With our malfunction, we find that the output of each key is being replaced by another letter/character that is one place to the right.

Question: Could Luisa use this malfunction to send encrypted messages to her

friends?

This is Computational Thinking

As a result of the malfunction, you have to know the location and relative position of the letters you want to type. In particular, which character is to the left and the right, and what happens when it comes to letters that are located at the beginning of the row. We apply Abstraction to understand the logic of of the problem.

Once we understand the logic, we can design an algorithm that helps us solve to solve the problem. Do the following for each word:

Step 1 – Find the letter on the keyboard

Step 2 – If the letter is not at the beginning of the row, then type the letter to the left. Else, type the letter at the end of the row

Step 3 – Repeat these steps for each letter in the word

Using the results of our algorithm, we can determine the correct solution.

Abstraction and algorithmic thinking are two important aspects of computational thinking.

B) is correct because each side of each part matches.

A) is incorrect because there are no stripes on the bottom part

C) is incorrect because on the left hand side of the dark part there is not a part, which is

lightly colored.

D) is incorrect. According to the image in the task the blue and the light must be connected, which they are not in this image.

This is Informatics

To solve this task, we must identify the properties of the parts of the gift package that remain the same when the gift package is unfolded and possibly rotated. Because of these movements, it’s best to consider the positions of the parts of the gift package relative to each other. For example, the blue part’s left-hand neighbor is the light part when looking from below the gift package. This kind of pattern matching is also used in computer vision systems to recognize different objects and to decide if objects in two photos or two videos may be the

same. Identifying objects based on their surface characteristics is a fundamental problem in computer vision. This could involve classifying objects into categories based on their surface shapes, such as distinguishing between different types of vehicles, animals, or household objects.

Increasingly, computer vision is being used in sports for example to track players on a

field and analyze their performance.

ition remains unchanged).

This is Computational Thinking

The task requires a student to apply abstraction. Firstly, the student identifies information related to the task (the sequence of parts in the gift package). Then, the student activates spatial reasoning (when changing the way the gift package’s parts are represented, their position remains unchanged).

The correct answer is C)

Only animals of the same type arrive together.

Only the springbok uses the salt block. Only the ostrich eats the corn. The giraffe is the only one that does not eat the lucerne but eats the tree leaves. Only the springbok can eat the lucerne and the bush leaves. Only the warthog digs for roots.

Answer A is wrong because the giraffe does not eat lucerne or corn.

Answer B is wrong because the third animal, the warthog does not eat the bush leaves (it is

too short) and subsequently, the springbok cannot dig for roots.

Answer D is wrong because already the first animal, the giraffe, does not go for the lucerne or the salt block (it could not bend so much down to the ground)

This is Informatics

In this task you are not asked to find a solution, you are tasked with verifying multiple solutions and see which one follows the given constraints.

Complex tasks can have various conditions that are combined with AND or OR. Combining “A AND B” means that both conditions have to be true. While “A OR B” means that just one of the conditions has to be satisfied. Restrictions are specified with NOT to indicate that the negation of a condition must be true.

This is Computational Thinking

Decomposition: The task requires students to breakdown the task per animal and identify their preferred food before determining their order.

Logical reasoning: The task requires students to reason out a conclusion based on the restrictions and conditions provided.

Correct answer is D) S, E, E, S

All paths of different colors and different styles are shown in the picture.

The correct path (D) to the treasure is shown on the picture by green path. All other paths (yellow (A), blue (B), and red dashed (C)) lead the pirate into the sea. The pirate would be on one of the X mark in the sea at end of the first, second, or third instruction step.

We don’t need to know how long a mile is on the picture. It can be understood from the task statement that the four steps are all of equal distance. Since all answers contain two E’s and two S’s, an invisible 2x2 grid can be drawn with the pirate and the treasure box as two diagonally opposite corners. It is easy to see that only by going through the center point, can the pirate avoid falling into the sea.

This is Informatics

Maps are often represented in computer science as graphs with vertices and edges that connect the vertices. Algorithms are often developed based on the graph data structure to solve various problems. In this task, the invisible map contains 9 vertices and 12 edges with an additional constraint that the edges run on horizontal and vertical directions only. Movement in the given instruction corresponds to traversing the graph from one vertex to another along

the connecting edge.

This is Computational Thinking

This task requires some algorithmic thinking to decide which algorithm (sequence of instructions) achieve the goal (getting to the treasure chest) while meeting the constraint (not falling into the sea). A certain amount of decomposition is also necessary because the solver needs to imagine how the answer, the code of type E, E, S, S consists of two instructions E, S (which are not described exactly because we don’t know how much is 1 mile in the picture) and how the movement of the pirate really looks like.

A certain spatial imagination is also needed to solve the task – we have to imagine that the pirate will move on a square which opposite vertices are positions of the pirate and the treasure. And we can see that the way on the perimeter of the square must go through the sea. But, yes, spatial imagination is not a part of computational thinking.

Correct answer is 18 (actions).

This is the sentence that correctly states what the picture shows:

“Tom has two apples and four limes but Mary has three apples and three bananas.”

To use the smallest number of actions, we need to remove words from the incorrect sentence in such a way that the highest possible number of words remain.

Working from left to right along the sentence, we find that there are 6 words that already occur in the order we need them in to construct the correct sentence:

“Tom has three apples and two limes but Mary has four apples and four bananas”

These can be left at the beginning of the sentence by deleting the other words that are not highlighted.

“Tom has three apples and two limes but Mary has four apples and four bananas.”

The correct sentence does have the same number of words as the wrong one, however. Hence, the deleted nine words need to be replaced by new words in the correct order from the word bank. So we need to delete nine words and then add nine words to replace the previously deleted words. We need to perform a total of 9 + 9 = 18 actions.

This is Informatics

It is clear from the outset that there is a simple brute-force method for fixing any error in the context of this problem: return all words to the word bank and start again! The challenge here is to find the optimal solution – that is, finding the one (or ones) which use the least number of steps. Optimisation is an important part of computer programming, though the ultimate efficiency of a program often needs to be weighed against the cost (in time and/or money) of discovering more efficient solutions.

The systematic ordering of lists subject to certain rules is a well-studied area of algorithms and informatics. The structure used in this problem is a modified stack, where elements can be removed from anywhere but only added to the top (at the end of the sentence).

This is Computational Thinking

This task requires some computational thinking, especially evaluation skills. The solver needs to find optimal solution which is in case he/she doesn’t know the exact appropriate algorithm for finding it an evaluation problem e.g. how to find the condition which shows us whether some word is a candidate for removing from the sentence or not.

Also some decomposition skills are required. The solver can split the solution to two basic steps: first to remove some words and then to add remaining words.

Answer: E. Hannah

Based on the what can be seen on the computer screen, we know who each student sits next to.

From the view below, we know that James is sitting next to Emma.

From the view below, we know that Emma is sitting between James and Diana.

Using the same method with the rest of the views, we can see all 9 students in this order:

The one who sits in the middle is the one at the 5th position from left, or the 5th position from right.

That person is Hannah.

This is Informatics

This task presents an example in which streaming software for an online class arranged the students as separate tiles in an arbitrary way. We are asked to find the correct order to discover who is sitting in the middle.

The data structure of the students arrangement is called ‘doubly linked list’. In a doubly linked list each node of the list contains the element, a reference to the previous node, and a reference to the next node. In this task, each screen (node) shows the child (element of the list) and references for the child on the right and on the left of the child in the center of the screen. This task includes an exercise in traversing a list, starting from either end.

This is Computational Thinking

Computational thinking in this task refers to the use of logical thinking to solve it. This involves understanding the problem, creating an algorithmic approach to evaluate the conditions, and then applying the logic to the given scenario. Logical thinking is necessary to find the solution. It involves breaking down a problem into steps in order to find a solution. If you’ve ever looked up guides on putting together puzzles, you might find the specific pattern of piece connections, find the edge pieces, sort by shape, and work section by section.

The background shown in answer C is not completely built according to the diagram.

A tile with a diamond on it can only be followed by , which is not the case here. 

There are several ways to find the solution of this task. A straightforward strategy is to try each given background image and check each tile against the diagram to see if it is valid. The quickest way is this: You check the tiles in the diagram starting with the tiles from which only one arrow emanates. Think of theses arrows as constraints. A → B means “Tile A must be followed by Tile B”. Then check if this constraint holds for each background image.

This is Informatics

Some computer games – like endless runner games – have a background that scrolls horizontally, creating the illusion that the player moves through a fantasy game world. Sometimes, the background is not a constant image, but is automatically created by the computer. This is called procedural generation. Usually smaller elements are randomly combined to create a huge variety of backgrounds. However, the combination of elements cannot be completely random but must obey certain rules to avoid situations the player cannot cope with. In the task, such rules are represented by a diagram made of tiles and arrows. This is called a directed graph. Graphs are used for all kinds of modeling.

This is Computational Thinking

To solve the task, a contestant must read and use the directed graph. The graph determines

the composition of the background image. It can be seen as an abstraction of the mechanism automatically generating images. Additionally, pattern recognition needs to be used to visually divide the background as a series of image blocks and recognize faulty transitions.

Therefore, this task involves algorithmic thinking, abstraction, and pattern recognition.

Oliver’s rattle is in picture A).

When balls go through the rattle, they cannot change their order. So you only need to check the order of all balls. After the red ball comes the yellow one , after the yellow one is the green one . After the green one is the blue one and after the blue one is the purple one . After the purple ball there is the red one again. Let’s look at the order of the balls starting from the red one. When we reach the end, we will go back to the start.

In answer A), the balls are in the correct order.

In answer B), there is the blue ball after the yellow one, but there should be the green ball.

In answer C), the red and the yellow ball are not together.

In answer D), even though the red and the yellow ball are together, they are in a different direction.

This could be OK, if we flip the rattle, as it is a see-through from both sides. But before the yellow ball, there is the purple ball instead of the green one.

This is Informatics

In this task, Oliver’s rattle illustrates the operating principle of a circular linked list. In this list, each element has a so-called pointer to the next element, and the pointer of the last element in the list points to the first element, thereby forming a circle. A circular linked list can

store anything. In this task, a circular linked list is called a 'rattle', and the items stored are 'colorful balls'.

That means, in this task, we know for each ball which ball is next. When we check the order of the balls, we can start from any ball and need to go through all of them (the whole list) in the correct order.

There are many areas in real life where we encounter circular linked lists. One such area is the music playlists. You've probably listened to songs in a playlist and wanted them to play one after another. After all the songs in the playlist finish playing, they start over from the first song.

There are some benefits when we used a circular list to store our items. The first benefit is that in a circular list there is no end point. Since it loops back to the beginning, you never run out of elements to check or use. The second benefit is the efficiency in navigation. It is easy to move through the list without needing special rules for the end. You just keep going in one direction.

This is Computational Thinking

To solve this task, you need to look at the order of the balls and find the option where the balls are in the same order as in the original image. This is called pattern recognition. Recognizing patterns is helpful to determine if some problems are similar or even the same. Then, we don’t need to solve each of them separately, instead we can use the solution to one of them to help us solve the other.

Answer D is correct: 6 beads.

We can make up all Bebracelets that can be made in this case and see which ones have the largest number of beads. 

The first bead from the tube has number 5. If it is put on the string, only beads 6, 7, 8, and 9 can be put on the string afterwards, with two possible bead sequences that can be on the string in the end: 5679, and 589. If bead 5 is put aside, and the next bead (1) is put on the string first, there are more and longer possible sequences, as shown here:

If any other bead is put on the string first, the longest possible final sequence is already included in one of those above, starting with either #1 or #5. For example, putting bead #2 on the string first leads to sequences such as 24679 or 2489, both of which are included in one of the longer sequences above (124679 and 12489, respectively).

From this, we figure out that the Bebracelets with the largest number of beads from the given tube start with bead 1 and consist of 6 beads each: 124679, and 123679.

This is Informatics

In computer science, a "sequence" refers to arranging pieces of data into a series, such as a character sequence (also known as string) or a number sequence. Each member of the sequence is called an element, and a subsequence is formed by selecting elements from the original sequence without changing the order of these elements.

Both the beads in the tube (in the order the beads are coming out of the tube) and the Bebracelets can be considered

sequences of the numbers on the beads, if other properties like shape and color are ignored. Then, this Bebras task asks

for finding a Longest Increasing Subsequence of the tube sequence, that is the longest subsequence with numbers going up only.

For sequences that are (much) longer than the tube sequence in this Bebras task, making up all possible increasing subsequences in order to find the longest ones will usually take too much time to be feasible. Fortunately, computer scientists developed efficient algorithms to find longest increasing subsequences quickly. The time used by such algorithms will be mostly in line with the length of the sequence: For sequences of length 1000, they will use in the order of 10000 steps, for sequences with a million elements, they will use in the order of 20 million steps – which is not much for a modern computer.

Problems related to finding specific subsequences often can be solved using a technique known as Dynamic Programming.

This is Computational Thinking

It would take a considerable amount of time to list all possible solutions for a task, and some of them may not even fulfill the task requirements. Therefore, finding a way to efficiently identify possible solutions and eliminate the impossible ones is key to solving the task. This is where algorithmic thinking comes into play.

Moreover, when deciding whether to string a bead, it is essential to evaluate how this decision might limit the selection of beads that can be used afterward. This requires simulating the impact of stringing a bead, such as how adding bead number 5 prevents beads 1 through 4 from being put on the string. This use of simulation is another aspect of computational thinking.

The correct answer is D.

The 1st ball will go down the most left-hand path. This will change the gate 1 and gate 2 to

the right.

As gate 1 has been changed, the 2nd ball will go to the right, but then left at the gate 3. This

will change gate 1 back to left and gate 3 to right.

The 3rd ball will be sent left at gate 1 and right at gate 2. This will change gate 1 to right and gate 2 to left.

The 4th ball will be sent to the right at gate 1 and will continue right at gate 3. This will change gate 1 and gate 3 to left.

The 5th ball will be sent down the left-hand path.

Answer A is incorrect because it will create this incorrect pattern:

Answer B is incorrect because it will create this incorrect pattern:

Answer C is incorrect because it will create this incorrect pattern:

This is Informatics

Computers use very small parts that work like these gates. They are called transistors and a

modern computer has billions of them inside to control where the electricity goes. In this task, all the gates were set to the left, but we can see how one gate affects the gates that follow. Transistors in a computer can be set to on or off, just like these gates are set to left or right. Imagine if you could control all the gates independently, wouldn’t the task be much easier?

That is how transistors in a computer work. By having an electrical charge or not, it can act like a switch to control a circuit. Transistors can also be used as a memory to store information in a computer, where if there is a charge in the transistor, it represents the digit 1, and if there is no charge it represents the digit 0.

This is Computational Thinking

Algorithms. This task illustrates the concept of following an algorithm. A simple programming language consisting of gates is defined, a specific algorithm with the arrangement and starting positions of three gates is presented, and the student must follow the algorithm for a specific input to solve the task.

The correct answer is BEAVERDAM.

From the task we know that if the alarm is sounded after n seconds, then the Burglar Beaver is guaranteed that the first n – 1 letters of his guess are correct and the nth letter is wrong. We illustrate this with an example:

• When the alarm sounds after 3 seconds, here's what happened:
• After 1 second, the first letter of the guessed code has been compared with the first letter of the secret code. The
• alarm not sounding means that the first letter of his guess is correct.
• After 2 seconds, the second letter has been compared. The alarm not sounding means that the second letter of his
• guess is also correct.
• After 3 seconds, the third letter has been compared . The alarm sounding means that the third letter of his guess is
• wrong.

Using this reasoning, we can construct a table to systematically identify the first letters of the secret code. The underlined letters in the "Guess" column refer to those that are guaranteed to be correct.

This is Informatics

In computer security, cryptography plays a crucial role in keeping sensitive information safe. This challenge introduces a concept known as side-channel attacks, a sophisticated approach used by hackers. This approach takes advantage of information leaked by the hardware rather than directly targeting a program. A timing attack uses the fact that the amount of time it takes for an algorithm to finish differs depending on the input. In this challenge, we have an algorithm that essentially performs a letter-by-letter comparison for password checking. The number of seconds before it determines that a password is incorrect, provides information about the number of correct characters.

To understand the threat posed by side-channel attacks, consider the following scenario. Suppose that the password is

"BEAVERDAM". A hacker can first try one-letter passwords. If the hacker tries "A" or "C", an alert is sounded after 1 second. But, if the hacker tries "B", an alert is sounded after 2 seconds, thereby revealing the first letter of the password. The hacker can continue this strategy and try two-letter passwords, then three-letter passwords, and so on. Assuming that the password consists only of capital letters from the English alphabet, this would mean that, even though there are theoretically over 5.4 trillion possible nine-letter combinations, the password can be correctly guessed after at most 26 ×

9 = 234 tries.

Other types of side-channel attacks include power analysis attacks, which rely on patterns in the device voltage while an

algorithm is running. Since some computations are more power-hungry than others, tracking power consumption makes it possible to determine the type of computation being performed and thus identify at which step an algorithm currently is. In addition, a cache-based side-channel attack exploits patterns related to accessing the cache, a small section of the computer memory that enables extremely fast retrieval of frequently accessed data.

Defending against side-channel attacks can be really difficult since they are invisible to the user, they do not leave

traces, and they use features that are built in the very design of the hardware. For example, the 2018 security vulnerabilities called Spectre and Meltdown, which allowed for cache-based side-channel attacks, affected virtually every Intel processor built after 1995 and forced Intel to redesign its microprocessors.

This is Computational Thinking

An important skill that is used in this task is decomposition. To get an answer to this task, the problem can be divided into subproblems, each involving guessing a portion of the secret code. By solving each subproblem independently and combining the results, we can determine the complete secret code. The burglar uses a computational thinking skill called analytical thinking to figure out the password. By breaking down the problem into smaller parts, the burglar is able to discover the necessary letters and understand the relationships between them.

Correct answer: 16

16 beavers went to the Forest.

To figure out how many beavers have taken each path, we marked the intersections with letters A, B, …, F. Because a beaver can move on each path only in one direction, shown by the arrow, each beaver can visit each intersection only once.

The beavers that went to the forest must have gone through F or E. To get to F, one must arrive through C or D. We know that 4 beavers arrived from C (and thus do not even need to backtrack further from C). However, we do not know how many arrived from D.

Let's look at the paths connected to intersection D. From a beaver’s house, there are 9 beavers that went to intersection D. So there are 9 beavers that have to leave intersection D. We can see that there are 3 paths leaving intersection D: D to C (2 beavers), D to E (6 beavers) and D to F, where the number is missing. Since there are 9 beavers leaving intersection D and there are already 2 + 6 beavers leaving, there is only one beaver that takes the D to F path (9 – (2 + 6) = 1).

Now let's look at path from F to Forest. We can see that there are 4 + 1 beavers that went to F: 4 beavers from C and 1 beaver from D. From F, 3 beavers went to the museum, which means that 2 beavers went to the forest (5 – 3 = 2).

We still need to find out how many beavers went to the Forest from intersection E. There are 6 beavers that went from D to E and because 8 beavers went to B from the house, 8 beavers went from B to E as it is the only way. In total, 6 + 8 = 14 beavers went to E, which means that 14 beavers went from E to the Forest as this is the only path available.

Summing up the numbers of beavers that went from F to Forest and from E to Forest, there are 2 + 14 = 16 beavers went to Forest. The final answer is 16.

This is Informatics

This challenge involves a concept from graph theory called a weighted directed graph. The

arrows indicate the allowed direction in the weighted graph.

In a weighted graph, each edge has a number attached to it, representing its weight. This

weight can signify various things, like the length of a road or the frequency of traversal along that path. For instance, in this challenge, the numbers on the paths indicate how many times a beaver has travelled along that path.

Additionally, the challenge utilizes the concepts of in-degree and out-degree in graph theory. In-degree refers to the sum of weights of inbound edges to a node, while out-degree refers to the sum of weights of outbound edges from a node.

To solve this problem, participants need to determine the paths not explicitly indicated

starting from the beaver's home. This involves analysing the in-degree and out-degree of the

paths to infer the remaining routes taken by the beavers.

This is Computational Thinking

We use abstraction to model the problem. The map is drawn using a graph, the paths

between villages are represented as lines. Using abstraction also helps us solve the

problem. Knowing how to interpret an abstraction is part of computational thinking.

Decomposition: the initial task is to find the number of all paths, this task can be decomposed when filtering the data by considering the traversal of each path.

Iterative reasoning: the task requires inferring the missing routes taken by the beavers. To accomplish this, we need to develop a systematic approach by observing patterns and considering the in-degree and out-degree of nodes, reasoning about possible routes, and deducing the likely number of beavers that have taken the path.