Interview Questions

Puzzles Back

You are standing next to a well, and you have two jugs. One jug has a content of 3 liters and the other one has a content of 5 liters. How can you get just 4 liters of water using only these two jugs?
Ans:  Fill the 5 liter jug. Then fill the 3 liter jug to the top with water from the 5 liter jug. Now you have 2 liters of water in the 5 liter jug. Dump out the 3 liter jug and pour what's in the 5 liter jug into the 3 liter jug. Then refill the 5 liter jug, and fill up the 3 liter jug to the top. Since there were already 2 liters of water in the 3 liter jug,1 liter is removed from the , 5 liter jug, leaving 4 liters of water in the 5 liter jug.
Solution 2:
Fill the 3 liter jug and pour it into the 5 liter jug. Then refill the 3 liter jug and fill up the 5 liter jug to the top. Since there were already 3 liters of water in the 5 liter jug, 2 liters of water are removed from the 3 liter jug, leaving 1 liter of water in the 3 liter jug. , Then dump out the 5 liter jug and pour what's in the 3 liter jug into the 5 liter jug. Refill the 3 liter jug and pour it into the 5 liter jug. Now you have 4 liters of water in the 5 liter jug.

In the middle of a round pool lies a beautiful water-lily. The water-lily doubles in size every day. After exactly 20 days the complete pool will be covered by the lily. After how many days will half of the pool be covered by the water-lily?
Ans: 

Because the water-lily doubles its size every day and the complete pool is covered after 20 days, half of the pool will be covered one day before that, after 19 days. Conclusion: After 19 days half of the pool will be covered by the water-lily.

Here are three answers: Answer A Answer A or B Answer B or C There is only one correct answer to this question. Which answer is this?
Ans:  If answer A would be correct, then answer B ("Answer A or B") would also be correct. If answer B would be correct, then answer C ("Answer B or C") would also be correct. This leads to the conclusion that if either answer A or answer B would be the correct answer, there are at least two correct answers. This contradicts with the statement that "there is only one correct answer to this question"., If answer C would be correct, then there are no contradictions. So the solution is: answer C.

A man has a wolf, a goat, and a cabbage. He must cross a river with the two animals and the cabbage. There is a small rowing-boat, in which he can take only one thing with him at a time. If, however, the wolf and the goat are left alone, the wolf will eat the goat. If the goat and the cabbage are left alone, the goat will eat the cabbage. How can the man get across the river with the two animals and the cabbage?
Ans:  First, the man takes the goat across, leaving the wolf with the cabbage. Then he goes back. Next, he takes the wolf across. Then the man goes back, taking the goat with him. After this, he takes the cabbage across. Then he goes back again, leaving the wolf with the cabbage. Finally, he takes the goat across. First, the man takes the goat across, leaving the wolf with the cabbage., Then he goes back. Next, he takes the cabbage across. Then the man goes back, taking the goat with him. After this, he takes the wolf across. Then he goes back again, leaving the wolf with the cabbage. Finally, he takes the goat across.

It's always 1 to 6, it's always 15 to 20, it's always 5, but it's never 21, unless it's flying. What is this?
Ans:  "It's always 1 to 6": the numbers on the faces of the dice, "it's always 15 to 20": the sum of the exposed faces when the dice comes to rest after being thrown, "it's always 5": the number of exposed faces when the dice is at rest, "but it's never 21": the sum of the exposed faces is never 21 when the dice is at rest, "unless it's flying": the sum of all exposed faces when the dice is flying is 21, when the dice is at rest, "unless it's flying": the sum of all exposed faces when the dice is flying is 21 (1 + 2 + 3 + 4 + 5 + 6)..

An old farmer died and left 17 cows to his three sons. In his will, the farmer stated that his oldest son should get 1/2, his middle son should get 1/3, and his youngest son should get 1/9 of all the cows. The sons, who did not want to end up with half cows, sat for days trying to figure out how many cows each of them should get. One day, their neighbour came by to see how they were doing after their father's death. The three sons told him their problem. After thinking for a while, the neighbour said: "I'll be right back!" He went away, and when he came back, the three sons could divide the cows according to their father's will, and in such a way that each of them got a whole number of cows. What was the neighbour's solution?
Ans:  The neighbour borrowed an extra cow, to make the total number of cows 18. Then the oldest son got 1/2 of 18 is 9 cows, the middle son got 1/3 of 18 is 6 cows, and the youngest son got 1/9 of 18 is 2 cows. Since 9+6+2 = 17, the cows could be divided among the three brothers in such a way that the borrowed cow was left over, and could be returned to its owner.

In front of you are 10 bags, filled with marbles. The number of marbles in each bag differs, but all bags contain ten marbles or more. Nine of the ten bags only contain marbles of 10 grams each. One bag only contains marbles of 9 grams. In addition, you have a balance which can weigh in grams accurate, and you are allowed to use it only once (i.e. weigh a single time). How can you find out in one weighing, which bag contains the marbles of 9 grams?
Ans:  Number the ten bags from 1 up to and including 10. Then take one marble from bag 1, two marbles from bag 2, three marbles from bag 3, etc. Place all 55 marbles that you selected from the bags together on the balance. The number of grams that the total weight of these 55 marbles differs from 550 grams, is equal to the number of marbles of 9 grams that are among those 55 marbles and that is , equal to the number of the bag which contains the marbles of 9 grams.

The numbers 1, 2, 3, 4, 5, 6, 7, 8, and 9 must be put in the depicted triangle, in such a way that the sums of the numbers on each side are equal. How should the numbers be arranged in the triangle?
Ans:  There are 18 solutions to this problem, when you leave out all rotations and mirror solutions. They are all listed below:
1
5 7
9 6
2 4 8 3
1
5 8
9 3
4 2 6 7
1
6 9
8 4
2 5 7 3
1
6 9
8 2
4 3 5 7
1
6 7
8 3
5 2 4 9
2
4 7
9 3
5 1 6 8
2
5 6
9 4
3 1 8 7
, 2
6 9
7 1
5 3 4 8
2
6 9
8 1
3 4 5 7
3
2 6
9 4
7 1 5 8
3
4 9
8 1
5 2 6 7
3
4 7
8 2
6 1 5 9
3
5 9
6 1
7 2 4 8
3
5 8
7 1
6 2 4 9
4
2 7
9 3
5 1 8 6
4
3 9
8 1
5 2 7 6
, 7
2 4
6 3
8 1 5 9
7
3 6
5 1
8 2 4 9.

A boy leaves home in the morning to go to school. At the moment he leaves the house he looks at the clock in the mirror. The clock has no number indication and for this reason the boy makes a mistake in interpreting the time (mirror-image). Just assuming the clock must be out of order, the boy cycles to school, where he arrives after twenty minutes. At that moment the clock at school shows a time that is two and a half hours later than the time that the boy saw on the clock at home. At what time did he reach school?
Ans: 

The difference between the real time and the time of the mirror image is two hours and ten minutes (two and a half hours, minus the twenty minutes of cycling). Therefore, the original time on the clock at home that morning could only have been five minutes past seven: The difference between these clocks is exactly 2 hours and ten minutes.

,

Conclusion: The boy reaches school at five minutes past seven plus twenty minutes of cycling, which is twenty-five minutes past seven!.

A long, long time ago, two Egyptian camel drivers were fighting for the hand of the daughter of the sheik of Abbudzjabbu. The sheik, who liked neither of these men to become the future husband of his daughter, came up with a clever plan: a race would determine who of the two men would be allowed to marry his daughter. And so the sheik organized a camel race. Both camel drivers had to travel from Cairo to Abbudzjabbu, and the one whose camel would arrive last in Abbudzjabbu, would be allowed to marry the sheik's daughter. The two camel drivers, realizing that this could become a rather lengthy expedition, finally decided to consult the Wise Man of their village. Arrived there, they explained him the situation, upon which the Wise Man raised his cane and spoke four wise words. Relieved, the two camel drivers left his tent: they were ready for the contest! Which 4 wise words did the Wise Man speak?
Ans: 

Take each other's camel.