Question

The ratio of the radii of two circles is 4:5. What is the ratio of the circumferences of the two circles?

Answer 1

Circumference = 2 x pi x radius

RADIUS 4                         RADIUS 5
C= 2 x pi x 4                   C = 2 x pi x 5
Both have 2 pi in them, so factor out leaving 4:5 still

Answer 2

The ratio of the radius of two circles is 4:5

C = 2πr

first circle
C = 8π

second circle
C = 10π

answer
ratio of radius 4:5, ratio of circumferences 8π: 10π