2024 AMC 8 Problem 9

Attempt Problem 9 of the 2024 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 2024 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 the marbles in Maria’s collection are red, green, or blue. Maria has half as many red marbles as green marbles and twice as many blue marbles as green marbles. Which of the following could be the total number of marbles in Maria’s collection?
2424
2525
2626
2727
2828
Answer: E
Concepts:ratio and proportiondivisibility
Small hint:
If red is rr, then green is 2r2r
Big hint:
Blue is twice green, so the total is a multiple of 77
Video solution:
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Written solution:
We can let rr be the number of red marbles that Maria has. Since Maria has half as many red marbles as green, then we know that she has 2r2r green marbles. Moreover, since she has twice as many blue marbles as green, then she will have 2(2r)=4r2(2r) = 4r blue marbles. Adding these together gives us r+2r+4r=7r, r + 2r + 4r = 7r, and so the answer must be a multiple of 7.7. Among the answer choices, only 2828 is a multiple of 7.7.
Thus, E is the correct answer.
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