"There are eight coins, they look exactly the same. One of them weighs slightly different from other seven. Now you are given a simple mechanical balance, which you can use no more than 2 times. How do you separate the different one from the pile. " keep 2 coins aside and devide remainaing 6 coins in 2 sets of 3, put each set in two plates of balance. If both are equal then the 2 unused ones can be weighed to find the heavier. If one set of 3 is heavier then weigh 2 out of three, and fine the heaviest one.