You have 10 camels each one carrying a basket containing 10 Ingots of Gold.
An Ingot of Gold weighs 1 pound.
You have been hoodwinked and discover that one of the camels is carrying imperfect gold. The Ingots on this camel weigh .9 pound each.
You have a scale that you can use once.
How do you discover which camel is carrying imperfect gold?
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There are three cowboys in a line such that the third cowboy can see cowboys 1 and 2. The second cowboy can see the first and the first can see no one.
All the cowboys are intelligent and reasonable.
I bring out a bag of hats containing 2 red hats and 3 blue.
I randomly place the hats on the three cowboys and tell them to shout as soon as they know the color of their own hat (which they obviously can not see).
After a few minutes the first cowboy shouts out.
What color is his hat? How did he know?
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There are 4 men who want to cross a bridge. They all begin on the same side.
You have 17 minutes to get all of them across to the other side. It is night. There is one flashlight. A maximum of two people can cross at one time. Any party who crosses, either 1 or 2 people, must have the flashlight with them. The flashlight must be walked back and forth, it cannot be thrown etc. Each man walks at a different speed. A pair must walk together at a rate of the slower man's pace.
Man 1: 1 minute to cross.
Man 2: 2 minutes to cross.
Man 3: 5 minutes to cross.
Man 4: 10 minutes to cross.
For example, if Man 1 and Man 4 walk across first, 10 minutes have elapsed when they get to the other side of the bridge. If Man 4 returns with the flashlight, a total of 20 minutes have passed, and you have failed the mission.
See how quickly you can solve this!
p.s. The flashlight cannot shine a long distance. No one can be carried, etc. (This is a straightforward problem. There are no tricks.)
ps #2: This question is asked at job interviews at Microsoft.