How to find the angle for a percentage of a circle - GRE Quantitative Reasoning

Card 1 of 24

0
Didn't Know
Knew It
0
1 of 2019 left
Question

An ant begins at the center of a pie with a 12" radius. Walking out to the edge of pie, it then proceeds along the outer edge for a certain distance. At a certain point, it turns back toward the center of the pie and returns to the center point. Its whole trek was 55.3 inches. What is the approximate size of the angle through which it traveled?

Tap to reveal answer

Answer

To solve this, we must ascertain the following:

  1. The arc length through which the ant traveled.

  2. The percentage of the total circumference in light of that arc length.

  3. The percentage of 360° proportionate to that arc percentage.

To begin, let's note that the ant travelled 12 + 12 + x inches, where x is the outer arc distance. (It traveled the radius twice, remember); therefore, we know that 24 + x = 55.3 or x = 31.3.

Now, the total circumference of the circle is 2πr or 24π. The arc is 31.3/24π percent of the total circumference; therefore, the percentage of the angle is 360 * 31.3/24π. Since the answers are approximations, use 3.14 for π. This would be 149.52°.

← Didn't Know|Knew It →