2001 AMC 10 Problem 19

Attempt Problem 19 of the 2001 AMC 10 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 2001 AMC 10 solutions, or check the answer key.

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19.

Pat wants to buy four donuts from an ample supply of three types of donuts: glazed, chocolate, and powdered. How many different selections are possible?

66

99

1212

1515

1818

Answer: D
Concepts:stars and barscombinations
Difficulty rating: 1340
Solution:

The number of selections is the number of nonnegative integer solutions of g+c+p=4.g+c+p=4. By stars and bars, this is (4+22)=(62)=15.\dbinom{4+2}{2}=\dbinom62=15.

Thus, the correct answer is D.

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