Sample Question #238 (brainteaser)
[This is a classic]
There are five bags containing the same number of coins. Four of the bags contain gold coins while the last bag contains silver coins coated with gold, and you are told that each gold coin weighs 10 oz. and each silver coin weighs 2 oz. less. You have a weighting scale (minimum=8 oz., maximum=large enough so you can weigh all five bags of coins) and you can take coins out of the bags. What’s the minimum number of weighings you need to do in order to tell which bag has the silver coins?
[I was asked this question at a State Street on-site a few years ago]