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2013 AMC 12B Problem 5

Problem 5 of 25EasierProbability & Statistics

The average age of 3333 fifth-graders is 11.11. The average age of 5555 of their parents is 33.33. What is the average age of all of these parents and fifth-graders?

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Solution

The parents’ ages sum to 55⋅3355\cdot 33 and the fifth-graders’ to 33⋅11,33\cdot 11, a total of 33⋅66.33\cdot 66. Dividing by 8888 people gives 33⋅6688=24.75.\dfrac{33\cdot 66}{88} = 24.75. Thus, the correct answer is C.
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