2010 AMC 10B Problem 3

Below is the professionally curated solution for Problem 3 of the 2010 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2010 AMC 10B solutions, or check the answer key.

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Concepts:pigeonhole principle

Difficulty rating: 720

3.

A drawer contains red, green, blue, and white socks with at least 22 of each color. What is the minimum number of socks that must be pulled from the drawer to guarantee a matching pair?

33

44

55

88

99

Solution:

To maximize the number of socks, we want to grab as many single socks as possible before getting a pair.

There are 44 colors, which means that we can draw one sock of each color before drawing a pair.

This means that it takes at least 4+1=54 + 1 = 5 socks to be drawn before a pair is guaranteed.

Thus, C is the correct answer.

Problem 3 in Other Years