Read the following SAT test question and then click on a button to select your answer.

The figure on the left shows a sector of a circle with center D. If the area of the sector is 500 square units and the length of arc ABC is 40 units, what is the radius of the circle?
The formula for the area of a circular sector is A=1/2θr^2 , where A is the area, θ is the central angle of the sector in radians, and r is the radius.

The formula for the length of a circular arc is s=rθ, where s is the arc length, r is the radius, and θ is the central angle formed by the arc in radians.

A.12.5
B.16
C.20
D.25

来源:可可英语 http://www.kekenet.com/sat/202003/606110.shtml