A set of five coins contains two that weigh 31g, two that weigh 33g, and one that weighs 32g. Using a balance scale just two times positively identify the weight of at least one coin.
Weigh two coins on each side
Case 1: The sides balance. They both have a 31g and a 33g coin
The unused coin must be 32g.
Case 2: One side is heavier. It has at least one 33g coin.
Test the two coins from the heavier side against each other.
The heavier one is 33g, if they balance they are both 33g.
Posted by Jer
on 2016-01-04 10:10:44