Five concentric circles with radii 1, 2, 3, 4, and 5 are drawn as shown dividing the circle of radius 5 into five regions: a circle of radius 1 and 4 annuuli (rings). What is the probability that a point chosen randomly from within the circle of radius 5 lies in the annulus whose inner radius is 3 and who outer radius is 4?

Answer 1

the area of C5 = 25π
The area of the annulus between C3 and C4 is 16π-9π = 7π

so, p = 7/25