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puzzles & brain teasers

Logic brain teasers

1. You are at a game show and there are three closed doors. There is a prize hidden behind one of the doors and the game show host knows where it is. You are asked to choose a door. The game show host then opens one of the other two doors showing that it is empty and asks you if you would like to change your selection. Should you stick to your original selection?

It is better if you select the other door. Since there are three doors then there is a 67% chance that you choose the wrong door with your first selection. If you are wrong the game show host will select the other wrong door since she knows where the prize is hidden. Therefore it is better if you switch to the door which the game show host leaves closed.

2. You are in a race and you overtake the person who is in second place. What is your position now?

You are in second place since you overtook the second runner and took her place!

3. Six drinking glasses stand in a row, with the first three full of juice and the next three empty. By moving only one glass can you arrange them so empty and full glasses alternate?

Pour the second glass into the fifth glass.

4. A man is asked what his daughters look like. He answers, "They are all blondes, but two, all brunettes, but two, and all redheads, but two." How many daughters did he have?

Three.. one blonde, one brunette and one redhead.

5. Why is it better to have round manhole covers than square ones?

1. Because manholes are round.
2. A round manhole cannot be dropped down the manhole.
3. Manhole covers are easier to transport (they roll).
4. They are cheaper to manufacture (they have a smaller surface area).
5. Circles have a consistent diameter, therefore if you have a large object or tool that you need to get down, you don’t have to move it to fix exactly in a square’s largest spot (the corners).

6. There is a waterlily in a pond, that doubles in size every day. If it takes the waterlily 180 days to cover the entire pond, how long does it take to cover half the pond?

179 days.