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Well-known corporations – Google, Intel or Apple – are famous for giving tricky tasks to applicants during the interview. We have collected 10 interesting examples of such tasks. Some of them were offered by the companies themselves, and some were posted by users who had already been interviewed. To solve them, knowledge of mathematics at the school level or just ingenuity is required.

Let’s see how you would handle such an interview.

What Apple is asking

10 задач с собеседований в крупные компании

Task 1.

Logic challenge. Sheldon Cooper (the same brilliant physicist from the popular series) reached the last frontier in a game quest in pursuit of treasure. In front of him are two doors, one leading to a treasure, the other to a deadly labyrinth. There is a guard at each door, each of them knows which door leads to the treasure. One of the guards never lies, the other always lies. Sheldon does not know which of them is a liar and which is not. Before choosing a door, you can ask only one question and only one guard.

Question: What to ask Sheldon at the guard to get to the treasure?

You can ask anyone, while asking the question like this: “Which door, according to the other guard, is the right one?”. If he asks the truthful, he will receive information about which door leads to the labyrinth, because a lying guard always lies. If he asks the lying guard, again, he will find out which door leads to the labyrinth, because he will lie about the door that the truthful guard will point to.

Task 2.

The earth has been invaded by aliens. They plan to destroy the entire planet, but decided to give humanity a chance. They chose ten of the smartest people and placed them in a completely dark room, sitting in a row, one by one. Each of the people was given a hat, hats of only two colors – pink and green. After all the hats are on their heads, the light turns on.
The alien starts at the last person in the row and asks what color the hat is on his head. Other words, except for the color of the hat, cannot be pronounced. Silence – too. If he answers correctly, he stays alive, if he makes a mistake, he is killed.
You can’t see what color your hat is, but you can agree on a certain principle by which to answer everyone. The location of the hats is random, the combinations can be any, you can see all the hats that are located in front of you.

Question: What should be answered so that as many people as possible survive?

The first responder counts the number of green hats in front of him: if this is an odd number, he calls “green”, if it is even – “pink”. The next, seeing the number and color of hats in front of him, can thus calculate what color the hat is on his head (for example, if green is still an odd number, then it is obvious that he is wearing pink), and so on. Thus, 9 out of 10 are guaranteed to survive, and the first person to answer has a 1 to 1 chance.

What Adobe asks

10 задач с собеседований в крупные компании

Task 3.

You have 50 motorcycles with a full tank of fuel, which is enough for a 100 km ride.

Question: Using these 50 motorcycles, how far can you go (given that they are initially located at a conditionally one point in space)?

The simplest answer is to start them all at the same time and drive 100 km. But there is another solution. First move all motorcycles 50 km. Then pour the fuel from half of the motorcycles into the other half. You thus have 25 motorcycles with a full tank. Drive another 50 km and repeat the procedure. So you can climb 350 km (not taking into account the fuel that will remain from the “extra” motorcycle when section 25 is in two).

What Microsoft asks

10 задач с собеседований в крупные компании

Task 4.

You have an endless supply of water and two buckets – 5 liters and 3 liters.

Question: How do you measure 4 liters?

Fill a five-liter bucket with water and pour some of the water into a three-liter bucket. You now have 3 liters in a small bucket and 2 in a large one. Empty the small bucket and pour the remaining 2 liters from the large one into it. Fill the large bucket again and pour water from it into the small one. There is already 2 liters of water in there, so you will have to add a liter, and 4 liters will remain in the large one.

Task 5.

You have two pieces of rope. Each one is such that if you set it on fire from one end, it will burn for exactly 60 minutes.

Question: Having only a box of matches, how to measure 45 minutes with the help of two pieces of such a rope (you cannot tear the ropes)?

One of the segments is set on fire from both ends, at the same time the second segment is set on fire, but from one end. When the first segment burns out completely, 30 minutes will pass, from the first segment there will also be a 30-minute segment. Setting fire to it from both ends, we get 15 minutes.

What Google asks

10 задач с собеседований в крупные компании

Task 6.

You have 8 balls of the same type and size.

Question: How to find the heavier ball using a balance and only two weighings?

Select 6 balls, divide them into groups of 3 balls and put them on the scales. The group with the heavier ball will win over the bowl. Choose any 2 balls from this trio and weigh. If a heavy ball is among them, you will know it; if they weigh the same, the heavy one that remains. If there was no heavier ball in groups of 3 balls, it is among the 2 remaining ones.

What Qualcomm asks

10 задач с собеседований в крупные компании

Task 7.

This task was described by a user who was interviewed for the position of senior systems engineer. He noted in the task description that he had his own answer, about which he argued for a long time with the interviewer.

Let’s say we have 10 packet data transfers over the wireless network. The channel is not very good, so there is a 1/10 chance that the data packet will not be transmitted. The transmitter always knows whether the data packet was successfully or unsuccessfully transmitted. When a transmission fails, the transmitter will transmit the packet until it succeeds.

Question: What channel capacity do we get?

According to the user, the answer should have been: 9 packets per second. But the person who conducted the interview did not agree with him, however, he did not give an answer, but repeated that “because of the retransmission, the throughput must be reduced by more than 1/10.”

What is asked in “Yandex”

10 задач с собеседований в крупные компании

Task 8.

This task was proposed to be solved for entering the School of Data Analysis in February 2014.
The game consists of identical and independent rounds, each of which wins with probability p. When the player wins, he gets $1, and when he loses, he pays $1. As soon as his capital reaches N dollars, he is declared the winner and removed from the casino.

Question: Find the probability that the player will lose all the money sooner or later, depending on his starting capital K.

Task 9.

This problem was asked to developers in an interview, and it is more directly related to programming than the previous examples.

There is a morphological dictionary with about 100,000 entries, in which the perfective and imperfective verbs are placed in separate entries (that is, “do” and “make” are considered different dictionary entries). You need to find such species pairs in the dictionary and “glue” the entries into one.

Question: Describe the general scenario for solving such a problem and an approximate algorithm for searching for species pairs.

Unfortunately, we do not have answers to the Yandex tasks.

And bonus

Task 10.

This task is attributed to Albert Einstein – allegedly with its help he selected his assistants. Another almost legendary story attributes authorship to Lewis Carroll. Note that it is very easy to solve on paper, but if you want hardcore, try to solve it in your head.

There are five houses on the street.
The Englishman lives in the red house.
The Spaniard has a dog.
They drink coffee in the green house.
The Ukrainian is drinking tea.
The green house is immediately to the right of the white house.
Whoever smokes Old Gold breeds snails.
Kool is smoked in the yellow house.
Milk is drunk in the central house.
The Norwegian lives in the first house.
The neighbor of the one who smokes Chesterfield keeps a fox.
Kool is smoked in the house next door to the one where the horse is kept.
Anyone who smokes Lucky Strike drinks orange juice.
A Japanese smokes Parliament.
The Norwegian lives next to the blue house.

Each of the houses is painted in a different color, a representative of a different nationality lives in each house, each has its own pet, its own favorite brand of cigarettes and drink.

Question: Who drinks water? Who is holding the zebra?

The Japanese holds a zebra, the Norwegian drinks water.


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