2005 AMC 12A Problems/Problem 5

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Problem

The average (mean) of 20 number is 30, and the average of 30 other numbers is 20. What is the average of all 50 numbers?

$(\mathrm {A}) \ 23 \qquad (\mathrm {B}) \ 24 \qquad (\mathrm {C})\ 25 \qquad (\mathrm {D}) \ 10 \qquad (\mathrm {E})\ 27$

Solution

$\frac{20 \cdot 30 + 30 \cdot 20}{50} = 24 \ \mathrm{(B)}$

See also

2005 AMC 12A (ProblemsAnswer KeyResources)
Preceded by
Problem 4
Followed by
Problem 6
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All AMC 12 Problems and Solutions