Question

A dartboard consists of two concentric circles. The probability of hitting the inner circle is

64%. If the outer circle has a diameter of 20 inches, what is the radius of the inner circle?

2 inches
4 inches
8 inches
16 inch

Answer 1

Given:
Diameter of outer circle = 20 inches.

We need to find the Area of the outer circle to get the radius of the inner circle.

Area = πr²

Outer circle Area = 3.14 * (10in)² = 314 in²

314 in² * 64% probability = 200.96 in² Area of the inner circle.

200.96 in² = 3.14 * r²
200.96 in² / 3.14 = r²
64 in² = r²
√64 in² = √r²
8 in = r

radius of inner circle is 8 inches.