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2009 AMC 10A Problem 18

Problem 18 of 25IntermediateAlgebraCounting & Probability

At Jefferson Summer Camp, 60%60\% of the children play soccer, 30%30\% of the children swim, and 40%40\% of the soccer players swim. To the nearest whole percent, what percent of the non-swimmers play soccer?

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Solution

Take 100100 children: 6060 play soccer, and 40%40\% of them, or 24,24, also swim. So 6024=3660 - 24 = 36 soccer players do not swim. There are 3030 swimmers and 7070 non-swimmers, so the fraction of non-swimmers who play soccer is 36700.51451%.\dfrac{36}{70} \approx 0.514 \approx 51\%. Thus, the correct answer is D.

More practice

Concepts: percentage · Venn Diagram · conditional probability

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