2017 AMC 10A Problems/Problem 15
Problem
Chloé chooses a real number uniformly at random from the interval . Independently, Laurent cooses a real number uniformly at random from the interval . What is the probability that Laurent's number is greater than Chloé's number?
Solution
Denote "winning" to mean "picking a greater number". There is a chance that Laurent chooses a number in the interval . In this case, Chloé cannot possibly win, since the maximum number she can pick is . Otherwise, if Laurent picks a number in the interval , with probability , then the two people are symmetric, and each has a chance of winning. Then, the total probability is