posted by Sarah .
Situation 1: You have eight billiard balls. One of them is "defective," meaning that it weighs more than the others. How do you tell, using a balance, which ball is defective in two weighings?
Situation 2: You have five jars of pills. All the pills in one jar only are "contaminated." The only way to tell which pills are contaminated is by weight. A regular pill weighs 10 grams; a contaminated pill is 9 grams. You are given a scale and allowed to make just one measurement with it. How do you tell which jar is contaminated?