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.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

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
Small hint:
Consider the worst case: draw as many as possible without ever reaching 1515 of one color
Big hint:
Take 1414 of each color that has at least 14,14, and all balls of the smaller colors
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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