Circles X and Y are concentric. If the radius of circle X is four times that of circle Y, what is the probability that a point selected inside circle X at random will be outside circle Y?  Choose the correct choice from the following.
A) 13 B) Pi/3 C) Pi/2 D) 15/16 E) 8/9
Small circle radius = a, so area = PI a ^ 2   Large circle radius = 4a, so area = 9. PI a ^ 2   Area of shaded region = 16PI a^2 - PI a^2 = 15 PI a^2   So, probability = ( 15 PI a^2 ) / (16 PI a^2 )   = 15/16= Answer = 15/16
<result>D</result>
Circles X and Y are concentric. If the radius of circle X is four times that of circle Y, what is the probability that a point selected inside circle X at random will be outside circle Y?