2009 AMC 8 Problem 19

Attempt Problem 19 of the 2009 AMC 8 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2009 AMC 8 solutions, or check the answer key.

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19.

Two angles of an isosceles triangle measure 7070^\circ and x.x^\circ. What is the sum of the three possible values of x?x?

9595

125125

140140

165165

180180

Answer: D
Concepts:isosceles triangleangle sumcasework
Difficulty rating: 1310
Solution:

All the following possibilities are shown below.

In the first scenario, we get x=70x = 70 by the properties of the isosceles triangle.

In the second scenario, we get that 702+x=180, 70 \cdot 2 + x = 180, from which we get that x=40.x = 40.

From the third scenario, we get that 2x+70=180, 2x + 70 = 180, from which we get that x=55.x = 55.

The sum of these values yields 70+40+55=165. 70 + 40 + 55 = 165.

Thus, D is the correct answer.

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