2017 AMC 8 Problem 9

Attempt Problem 9 of the 2017 AMC 8 below, then check your answer against the video solution and professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2017 AMC 8 solutions, or check the answer key.

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

9.

All of Marcy’s marbles are blue, red, green, or yellow. One third of her marbles are blue, one fourth of them are red, and six of them are green. What is the smallest number of yellow marbles that Marcy could have?
1 1
2 2
3 3
4 4
5 5
Answer: D
Concepts:fractionleast common multiple
Small hint:
The total number of marbles must be divisible by both 33 and 44.
Big hint:
Test the smallest multiples of 1212 until there is room for the 66 green marbles.
Video solution:
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Written solution:
If the number of marbles is divisible by both 33 and 4,4, then the number must be divisible by 12.12. If we test 12,12, we get that there are 44 blue marbles and 33 red marbles. This leaves a maximum of 55 green marbles, which is not possible.
If there are 2424 marbles, then there are 88 blue marbles and 66 red marbles. To find the number of yellow marbles, we get 24−8−6−6=4.24 - 8 - 6 - 6 = 4.
Thus, D is the correct answer.
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