PSAT Math Multiple-Choice Question 77: Answer and Explanation

Question: 77

Note: Figure not drawn to scale.

In the figure above, if triangle ABC is isosceles, what is the perimeter of the triangle?

• A. 12.5
• B.
• C.
• D.

Correct Answer: C

Explanation:

C

The question asks for the perimeter of an isosceles triangle. Use the geometry basic approach. Start by labeling the figure with the given information. The question says that the triangle is isosceles, and there is a right angle present in the figure. An isosceles right triangle has angles that measure 45°, 45°, and 90°. Since AB = 5, that means BC = 5 as well. Using the 45°-45°-90° right triangle rule, AC = 5. Therefore, the perimeter of the triangle is 5 + 5 + 5 or 10 + 5. The correct answer is (C).