Interview Questions
Puzzles
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There is a unique number of which the square and the cube together use all ciphers from 0 up to 9 exactly once. Which number is this? |
| Ans:
The number is 69: 69^2 = 4761 and 69^3 = 328509.. |
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The gentlemen Dutch, English, Painter, and Writer are all teachers at the same secondary school. Each teacher teaches two different subjects. Furthermore: Three teachers teach Dutch language There is only one math teacher There are two teachers for chemistry Two teachers, Simon and mister English, teach history Peter doesn't teach Dutch language Steven is chemistry teacher Mister Dutch doesn't teach any course that is tought by Karl or mister Painter. What is the full name of each teacher and which two subjects does each one teach? |
| Ans:
Since Peter as only one doesn't teach Dutch language, and mister Dutch doesn't teach any course that is tought by Karl or mister Painter, it follows that Peter and mister Dutch are the same person and that he is at least math teacher. Simon and mister English both teach history, and are also among the three Dutch teachers. Peter Dutch therefore has to teach next to math, also chemistry. ,teacher, he cannot be mister English or mister Painter, so he must be mister Writer. Since Karl and mister Painter are two different persons, just like Simon and mister English, the names of the other two teachers are Karl English and Simon Painter. ,Summarized: |
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Barbara has boxes in three sizes: large, standard, and small. She puts 11 large boxes on a table. She leaves some of these boxes empty, and in all the other boxes she puts 8 standard boxes. She leaves some of these standard boxes empty, and in all the other standard boxes she puts 8 (empty) small boxes. Now, 102 of all the boxes on the table are empty. How many boxes has Barbara used in total? |
| Ans:
By putting 8 boxes in a box, the total number of empty boxes increases by 8 - 1 = 7. If we call x the number of times that 8 boxes have been put in a box, we know that 11 + 7x = 102. It follows that x=13. In total, 11 + 13 × 8 = 115 boxes have been used. |
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A traveler, on his way to Eindhoven, reaches a road junction, where he can turn left or right. He knows that only one of the two roads leads to Eindhoven, but unfortunately, he does not know which one. Fortunately, he sees two twin-brothers standing at the road junction, and he decides to ask them for directions. The traveler knows that one of the two brothers always tells the truth and the other one always lies. Unfortunately, he does not know which one always tells the truth and which one always lies. How can the traveler find out the way to Eindhoven by asking just one question to one of the two brothers? |
| Ans:
The question that the traveler should ask is: "Does the left road lead to Eindhoven according to your brother?" If the answer is "Yes", the traveler should turn right, and if the answer is "No", the traveler should turn left. The traveler asks the question to the truth-telling brother, and the left road leads to Eindhoven. The truth-telling brother knows that his lying brother would say that the left road does not lead to Eindhoven, and so he answers "No". The truth-telling brother knows that his lying brother would say that the left road leads to Eindhoven, and so he answers "Yes". The traveler asks the question to the lying brother, and the left road leads to Eindhoven. The lying brother knows that his truth-telling brother would say that the left road leads to Eindhoven, and so he lies "No". ,The traveler asks the question to the lying brother, and the right road leads to Eindhoven. The lying brother knows that his truth-telling brother would say that the left road does not lead to Eindhoven, and so he lies "Yes". |
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Richard is a strange liar. He lies on six days of the week, but on the seventh day he always tells the truth. He made the following statements on three successive days: Day 1: "I lie on Monday and Tuesday." Day 2: "Today, it's Thursday, Saturday, or Sunday." Day 3: "I lie on Wednesday and Friday." On which day does Richard tell the truth? |
| Ans:
We know that Richard tells the truth on only a single day of the week. If the statement on day 1 is untrue, this means that he tells the truth on Monday or Tuesday. If the statement on day 3 is untrue, this means that he tells the truth on Wednesday or Friday. Since Richard tells the truth on only one day, these statements cannot both be untrue. ,Assume that the statement on day 1 is true. Then the statement on day 3 must be untrue, from which follows that Richard tells the truth on Wednesday or Friday. So, day 1 is a Wednesday or a Friday. Therefore, day 2 is a Thursday or a Saturday. However, this would imply that the statement on day 2 is true, which is impossible. ,From this we can conclude that the statement on day 1 must be untrue. This means that Richard told the truth on day 3 and that this day is a Monday or a Tuesday. So day 2 is a Sunday or a Monday. Because the statement on day 2 must be untrue, we can conclude that day 2 is a Monday. So day 3 is a Tuesday. Therefore, the day on which Richard tells the truth is Tuesday. |
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Assume that you have a number of long fuses, of which you only know that they burn for exactly one hour after you lighted them at one end. However, you don't know whether they burn with constant speed, so the first half of the fuse can be burnt in only ten minutes while the rest takes the other fifty minutes to burn completely. Also assume that you have a lighter. How can you measure exactly three quarters of an hour with these fuses? Hint: 2fuses are sufficient to measure three quarter of an hour Hint: A fuse can be lighted from both ends at the same time(which reduces its burning time significantly) |
| Ans:
With only two fuses that burn exactly one hour, one can measure three quarters of an hour accurately, by lighting the first fuse at both ends and the other fuse at one end simultaneously. When the first fuse is burnt out after exactly half an hour (!) you know that the second fuse still has exactly half an hour to go before it will be burnt completely, but we won't wait for that. ,We will now also light the other end of the second fuse. This means that the second fuse will now be burnt completely after another quarter of an hour, which adds up to exactly three quarters of an hour since we started lighting the first fuse!. |
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Tom has three boxes with fruits in his barn: one box with apples, one box with pears, and one box with both apples and pears. The boxes have labels that describe the contents, but none of these labels is on the right box. How can Tom, by taking only one piece of fruit from one box, determine what each of the boxes contains? |
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Tom takes a piece of fruit from the box with the labels 'Apples and Pears'. If it is an apple, then the label 'Apples' belong to this box. The box that said 'Apples', then of course shouldn't be labeled 'Apples and Pears', because that would mean that the box with 'Pears' would have been labeled correctly, and this is contradictory to the fact that none of the labels was correct. ,On the box with the label 'Appels' should be the label 'Pears'. If Tom would have taken a pear, the reasoning would have been in a similar way. |
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A light bulb is hanging in a room. Outside of the room there are three switches, of which only one is connected to the lamp. In the starting situation, all switches are 'off' and the bulb is not lit. If it is allowed to check in the room only once to see if the bulb is lit or not (this is not visible from the outside), how can you determine with which of the three switches the light bulb can be switched on? |
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To find the correct switch (1, 2, or 3), turn switch 1 to 'on' and leave it like that for a few minutes. After that you turn switch 1 back to 'off', and turn switch 2 to 'on'. Now enter the room. If the light bulb is lit, then you know that switch 2 is connected to it. If the bulb is not lit, then it has to be switch 1 or 3. Now touching for short the light bulb, will give you the answer: ,if the bulb is still hot, then switch 1 was the correct one; if the bulb is cold, then it has to be switch 3. |
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Jack and his wife went to a party where four other married couples were present. Every person shook hands with everyone he or she was not acquainted with. When the handshaking was over, Jack asked everyone, including his own wife, how many hands they shook. To his surprise, Jack got nine different answers. How many hands did Jack's wife shake? |
| Ans:
Because, obviously, no person shook hands with his or her partner, nobody shook hands with more than eight other people. And since nine people shook hands with different numbers of people, these numbers must be 0, 1, 2, 3, 4, 5, 6, 7, and 8. The person who shook 8 hands only did not shake hands with his or her partner, and must therefore be married to the person who shook 0 hands. ,The person who shook 7 hands, shook hands with all people who also shook hands with the person who shook 8 hands (so in total at least 2 handshakes per person), except for his or her partner. So this person must be married to the person who shook 1 hand. The person who shook 6 hands, shook hands with all people who also shook hands with the persons who shook 8 and 7 hands. ,The person who shook 5 hands, shook hands with all people who also shook hands with the persons who shook 8, 7, and 6 hands (so in total at least 4 handshakes per person), except for his or her partner. So this person must be married to the person who shook 3 hands. The only person left, is the one who shook 4 hands, and which must be Jack's wife. The answer is: Jack's wife shook 4 hands. |
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Yesterday evening, Helen and her husband invited their neighbours (two couples) for a dinner at home. The six of them sat at a round table. Helen tells you the following: "Victor sat on the left of the woman who sat on the left of the man who sat on the left of Anna. Esther sat on the left of the man who sat on the left of the woman who sat on the left of the man who sat on the left of the woman who sat on the left of my husband. Jim sat on the left of the woman who sat on the left of Roger. I did not sit beside my husband." What is the name of Helen's husband? |
| Ans:
From the second statement, we know that the six people sat at the table in the following way (clockwise and starting with Helen's husband): The remaining woman must be Anna, and combining this with the first statement, we arrive at the following situation:Helen's husband, Anna, man, Helen, Victor, Esther |