2016 AMC 10B Problem 7

Below is the professionally curated solution for Problem 7 of the 2016 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2016 AMC 10B solutions, or check the answer key.

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Concepts:ratio and proportionlinear equation

Difficulty rating: 1070

7.

The ratio of the measures of two acute angles is 5:4,5:4, and the complement of one of these two angles is twice as large as the complement of the other. What is the sum of the degree measures of the two angles?

 75 \ 75

 90 \ 90

 135 \ 135

 150 \ 150

 270 \ 270

Solution:

Let the smaller angle be x.x. Then, the larger angle is 54x.\frac 54 x. Note that their sum is 94x.\frac 94 x.

Their complements are then 90x90-x and 9054x.90 - \frac 54x. Since 90x90-x is larger than 9054x,90-\frac 54 x, we know 90x=2(9054x)90x=18052xx=60.\begin{align*}90 -x &= 2\left(90 - \frac 54 x\right) \\90-x&= 180-\frac 52 x\\x&=60.\end{align*}

Therefore, the sum is 9460=135.\dfrac 94 \cdot 60=135.

Thus, the correct answer is C .

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