2007 AMC 12B Problems/Problem 12

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Problem 12

A teacher gave a test to a class in which $10%$ (Error compiling LaTeX. Unknown error_msg) of the students are juniors and $90%$ (Error compiling LaTeX. Unknown error_msg) are seniors. The average score on the test was $84$. The juniors all received the same score, and the average score of the seniors was $83$. What score did each of the juniors receive on the test?

$\mathrm {(A)} 85$ $\mathrm {(B)} 88$ $\mathrm {(C)} 93$ $\mathrm {(D)} 94$ $\mathrm {(E)} 98$

Solution

Taking a weighted average

$(90\%)(83) + (10\%)(x) = 84$ where x is the Juniors' score

$\begin{align*}x & = 10(84 - .9(83) \\ & = 840 - 9(83) \\ & = 93 \Rightarrow \mathrm {(C)}$ (Error compiling LaTeX. Unknown error_msg)

See Also

2007 AMC 12B (ProblemsAnswer KeyResources)
Preceded by
Problem 11
Followed by
Problem 13
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All AMC 12 Problems and Solutions