Question

The ratio of the radii of two circles is 2:5.Then the ratio of their circumference is
a) 2:5 b) 5:2 c) 1:2 d) 4 : 10

Answer 1

let radius of 1st circle = 2x

let radius of 2nd circle = 5x

circumference of circle = 2πr

circumference of 1st circle = 2π * 2x = 4πx

circumference of 2nd circle = 2π * 5x = 10πx

ratio of their circumferences = 4πx = 2/5 = 2:5

10πx

Answer is (a) 2:5