1) What is the question you can ask all day, and no matter what the answers are, they would still be valid questions and correct?
Ans: What time is it?
2) Which part of London in France?
Ans: -N-
3) There are three switches downstairs. Each corresponds to one of the three light bulbs in the attic. You can turn the switches on and off and leave them in any position. How would you identify which switch corresponds to which light bulb, if you are only allowed one trip upstairs?
Ans: Keep the first bulb switched on for a few minutes. It gets warm, right? So all you have to do then is ... switch it off, switch another one on, walk into the room with bulbs, touch them and tell which one was switched on as the first one (the warm one) and the others can be easily identified .
4) A man who lives on the tenth floor takes the elevator down to the first floor every morning and goes to work. In the evening, when he comes back, he goes to the seventh floor and walks up three flights of stairs to his apartment. But on a rainy day, or if there are other people in the elevator, he goes to his floor directly. Can you explain why?
Ans: The man is a of short stature. He can't reach the upper elevator buttons, but he can ask people to push them for him. He can also push them with his umbrella.
5) How can you throw a ball as hard as you can and have it come back to you, even if it doesn't bounce off anything? There is nothing attached to it, and no one else catches or throws it back to you.
Ans: Throw the ball straight up in the air.
6) You are in a room with no metal objects except for two iron rods. Only one of them is a magnet.
How can you identify which one is a magnet?
Ans: Break one or both rods and the one who's pieces attract or repel eachother is your magnet.
7) Having 2 sand-glasses: one 7-minute and the second one 4-minute, how can you correctly time 9 minutes?
Ans: Turn both sand-glasses. After 4 minutes turn upside down the 4-min sand-glass. When the 7-min sand-glass spills the last grain, turn the 7-min upside down. Then you have 1 minute in the 4-min sand-glass left and after spilling everything, in the 7-min sand-glass there will be 1 minute of sand down (already spilt). Turn the 7-min sand-glass upside down and let the 1 minute go back. And that's it.
4 (4-min) + 3 (7-min) + 1 (4-min) + 1 (7-min) = 9
8) Given 27 table tennis balls, one is heavier than the others.What is the minimum number of weighings (using a two-pan balance scale) needed to guarantee identifying the heavy one? Of course, the other 26 balls weight the same.
Ans: It is enough to use a pair of scales 3 times.
Divide the 27 balls to 3 groups, 9 balls in each. Compare 2 groups – the heavier one contains the ball. If there is equilibrium, then the ball is in the third group. Thus we know the 9 suspicious balls.
Divide the 9 balls to 3 groups of 3. Compare 2 groups, and as mentioned above, identify the group of 3 suspicious balls.
Compare 2 balls (of the 3 possibly heavier ones) and you know everything.
So we used a pair of scales 3 times to identify the heavier ball.
9) What mathematical symbol can be placed between 5 and 9, to get a number greater than 5 and smaller than 9?
Ans: decimal point –> 5.9 or 5+(root of 9)=5+3=8
10) Two fathers and two sons sat down to eat eggs for breakfast. They ate exatly three eggs, each person had an egg. The riddle is fdor you to explain how?
Ans: one of the 'fathers' is also a grandfather. Therefore the other father is both a son and a father to the grandson. In other words, the one father is both a son and a father.
11) What digit is the most frequent between the numbers 1 and 1,000 (inclusive)? and What digit is the least frequent between the numbers 1 and 1,000(inclusive)?
Ans: The most common digit is '1'. and '0' is the least common digit even though 1,000 has three zero's !
Explanations for both riddles:
The digits 0 through 9 all follow the same pattern there is exactly 1 occurance of each digit for every ten numbers.
- For instance the digit 2 appears once between 10 and 19, at 12. And 2 appears once between, 30 and 39 at 32.
- However, each of the digits 1 through 9 also appear in other numbers in the tens and hundres place
Again, let's look at 2 which appears in 20,21,22, 23, etc.. as well as 200,201, 202,203..
So to figure out how to answer the first riddle you had to see what distinguishes the number 1? Only that we are including 1,000 which would be the first '1' in a new series of ten! In other words, the digit 1 only has a single extra occurance (301 occurences) compared to 2 or 3 or 9 which each have exactly 300 occurences.
12) Three lawyers rent a hotel room for the night. When they get to the hotel they pay the $30 fee, then go up to their room. Soon the bellhop brings up their bags and gives the lawysers back $5 because the hotel was having a special discount that weekend. So the three lawyers decide to each keep one of the $5 dollars and to give the bellhop a $2 tip. However, when they sat down to tally up their expenses for the weekend the could not explain the following details:
Each one of them had originally paid $10 (towards the initial $30), then each got back $1 which meant that they each paid $9. Then they gave the bellhop a $2 tip. HOWEVER, 3 • $9 + $2 = $29
The lawyers couldn't figure out what happened to the other dollar. After all, the three paid out $30 but could only account for $29.
Can you determine what happened?
Ans: There are many ways of explaining/thinking bout this truly brain bending riddle! It all boils down to the fact that the lawyers's math is incorrect. They did NOT spend $9 • 3 + $2.
They spent exactly $27 dollars. $25 for the room and $2 for the tip. Remember they got exactly $3, in total back.
Another way to think about the answer to this riddle is to just pretend that the bellhop refunded $3 to the lawyers (rather than giving them $5 and recieving $2 back). If the lawyers get $3 back and each takes $1. They they spent exactly $27 dollars.
13) Your job is to measure 45 minutes, if you have only two cords and matches to light the cords.Each cord burns from end to end in exactly one hour.
Ans: Start fire on both ends of one igniter cord and on one end of the second igniter cord. The very moment the first cord (where both ends burn) stops burning (that is after 30 minutes), start fire on the other end of the second cord (otherwise it would burn another 30 minutes). Thus the second igniter cord burns just 15 minutes from then. And that is all together 45 minutes.
14) You are one of 20 prisoners on death row with the execution date set for tomorrow. Your king is a ruthless man who likes to toy with his people's miseries. He comes to your cell today and tells you:
“I’m gonna give you prisoners a chance to go free tomorrow. You will all stand in a row (queue) before the executioner and we will put a hat on your head, either a red or a black one. Of course you will not be able to see the color of your own hat; you will only be able to see the prisoners in front of you with their hats on; you will not be allowed to look back or communicate together in any way (talking, touching.....).
The prisoner in the back will be able to see the 19 prisoners in front of him. The one in front of him will be able to see 18…
Starting with the last person in the row, the one who can see everybody in front of him, he will be asked a simple question: WHAT IS THE COLOR OF YOUR HAT?
He will be only allowed to answer “BLACK” or “RED”. If he says anything else you will ALL be executed immediately.
If he guesses the right color of the hat on his head he is set free, otherwise he is put to death. And we move on to the one in front of him and ask him the same question and so on…
Well, good luck tomorrow, HA HA HA HA HA HA!”
Now since you all can communicate freely during the night, can you find a way to guarantee the freedom of some prisoners tomorrow? How many?
Ans: First guy is a coin toss - let's wish him good luck.
His job is to establish the parity of black hats visible to him.
He says "Black" if he sees an odd number of black hats; "Red" otherwise.
By paying attention to what has been said, each prisoner will know his hat's color.
Example:
Second to speak hears "Black" and sees an even number of black hats.
He knows his hat is black [odd changed to even - must be his is black] and says "black".
Third guy has heard "black" and "black" and sees an even number of black hats.
He knows his hat is red [even stayed even - his hat can't be black] and says "red".
And so on, to the front of the line.
15) Three goddesses were sitting in an old Indian temple. Their names were Truth (always telling the truth), Lie (always lying) and Wisdom (sometimes lying). A visitor asked the one on the left: "Who is sitting next to you?"
"Truth," she answered.
Then he asked the one in the middle: "Who are you?"
"Wisdom."
Lastly, he asked the one on the right: "Who is your neighbor?"
"Lie," she replied.
And then it became clear who is who.
Ans: Let’s assign a letter to each goddess. We get these sentences.
1. A says: B is Truth.
2. B says: I am Wisdom.
3. C says: B is Lie.
First sentence hints that A is not Truth. Second sentence is not said by Truth either, so C is Truth. Thus the third sentence is true. B is Lie and A is Wisdom.
16) Teanchi and Beanchi are a married couple. They have two kids, one of them is a girl, what is the probability that the other kid is also a girl.
Ans: 1/3
This is a famous question in understanding conditional probability, which simply means that given some information you might be able to get a better estimate.
The following are possible combinations of two children that form a sample space in any earthly family:
Girl - Girl
Girl - Boy
Boy - Girl
Boy - Boy
Since we know one of the children is a girl, we will drop the Boy-Boy possibility from the sample space.
This leaves only three possibilities, one of which is two girls. Hence the probability is 1/3
17) Three boxes are all labeled incorrectly, and you must get the labels right. The labels on the boxes read as follows:
[box 1] nails
[box 2] screws
[box 3] nails and screws
To gain the information you need to move the labels to the correct boxes, you may remove a single item from one of the boxes. You may not look into the boxes, nor pick them up and shake them, etc.
Can this be done? If so, how? If not, why not?
Ans: Remove an item from box 3.
The item tells you what label to put on box 3.
Move the nails and screws label to the box labeled with the other item, and its label to the remaining box.
Example: you remove a nail from box 3.
Move the label nails from box 1 to box 3.
You can't move the nails and screws label to box 1: that would be a swap, and all three labels must be corrected.
Move it instead to box 2, and the screws label to box 1.
[box 1] screws
[box 2] nails and screws
[box 3] nails
Good Puzzles Collection:
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