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2012 AMC 12A Problem 4

Problem 4 of 25EasierAlgebra

In a bag of marbles, 35\dfrac{3}{5} of the marbles are blue and the rest are red. If the number of red marbles is doubled and the number of blue marbles stays the same, what fraction of the marbles will be red?

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Solution

Suppose there are 55 marbles: 33 blue and 22 red. Doubling the red gives 44 red while the blue stays at 3.3. The total is now 3+4=7,3 + 4 = 7, so the fraction that is red is 47.\dfrac{4}{7}. Thus, the correct answer is C.

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Concepts: fraction · ratio and proportion

Problem text and solution from the LIVE past-contest archive. See also the AoPS wiki page for community solutions.