2019 AMC 12A Problem 3

Attempt Problem 3 of the 2019 AMC 12A below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2019 AMC 12A solutions, or check the answer key.

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3.

A box contains 2828 red balls, 2020 green balls, 1919 yellow balls, 1313 blue balls, 1111 white balls, and 99 black balls. What is the minimum number of balls that must be drawn from the box without replacement to guarantee that at least 1515 balls of a single color will be drawn?

7575

7676

7979

8484

9191

Answer: B
Concepts:pigeonhole principle
Difficulty rating: 1020
Solution:

In the worst case, we draw 1414 each of red, green, and yellow, plus all of the blue (13),(13), white (11),(11), and black (9),(9), without reaching 1515 of any color.

That is 14+14+14+13+11+9=75 14 + 14 + 14 + 13 + 11 + 9 = 75 balls.

The next ball must complete a set of 15,15, so 7676 balls are needed.

Thus, the correct answer is B.

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