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Mr Smith has lots of pound coins, ten boxes in all. Each box contains 100 pound coins, but one box contains coins which are all counterfeit and are slightly lighter, 1/16 of an ounce lighter to be exact.
The problem lies in the fact that they all look identical, the only way to tell them apart is to weigh them.
Mr Smith knows the correct weight for a box, but how many weighings are required to determine which box contains the counterfeit ones?
Hint: The answer is a lot less than 100 weighings.
Answer: One weighing is enough.
Take one coin from the first box, two from the second and so on.
When the coins are weighed, the number of 1/16ths light will tell us which box contains the counterfeits.
For example if it was box 5, the weighing would be 5/16 too light.
These are the first 10 prime numbers (2, 3, 5...) prefixed with a 1.
Apparently, one side of a cat has more hair. The findings of the Swedish scientific establishment have been corroborated by a special enquiry by the BB Feline Federation. Many hair counts were taken of the side in question and consistently it was found to contain more hairs. The scientists determined that more hair was required on this side to insulate the cat from the elements while it was lying down. Perhaps you would like to examine a cat to confirm the findings. Before you do, can you guess which side of a cat has more hair?
Hint: Think laterally!
Answer: The outside!