2011 AMC 12B Problems/Problem 10

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Problem

Rectangle $ABCD$ has $AB=6$ and $BC=3$. Point $M$ is chosen on side $AB$ so that $\angle AMD=\angle CMD$. What is the degree measure of $\angle AMD$?

$\textbf{(A)}\ 15 \qquad \textbf{(B)}\ 30 \qquad \textbf{(C)}\ 45 \qquad \textbf{(D)}\ 60 \qquad \textbf{(E)}\ 75$

Solution

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Since $AB \parallel CD$, $\angle AMD = \angle CDM$ hence $CM=CD=6$. Therefore $\angle BMC = 30^\circ$. Therefore $\angle AMD=75^\circ$

See also

2011 AMC 12B (ProblemsAnswer KeyResources)
Preceded by
Problem 9
Followed by
Problem 11
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All AMC 12 Problems and Solutions