You have a 100 coins, that are silver on one side and gold on the other; both sides feel and taste the same so you can not distinguish between the silver face and the gold face by the sense of touch or taste. Is it possible to split the pile of coins in to two parts, where each halve has the same amount of gold face up as the other pile, if the only sense you can use is touch, and all you know is that there are 20 gold faces faced up and, hence 80 silver coin faces faced down?
Assumptions :
if one pile has 7 gold faces faced up, the other pile must have 7 gold faces up as well
you can not hear, smell, see or taste anything, but only can touch
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Take any 20 coins from the pile of 100 coins, and flip the pile over to get two equal piles - it really is that easy! For example, if you take 20 coins and 7 of them are gold facing up ways, then there will be 14 silver facing up ways coins, and also the other 14 gold facing up ways coins will be in the pile of 80 coins; if you flip the pile containing 20 coins, the 14 silver facing up ways coins will become 14 gold facing up ways coins, hence 2 piles containing an equal amount of gold facing up ways coins. This will work for any scenario, whether all the coins are in the pile of 20 coins, or none of them are in there.