The ratio of the radii of two circles is 9:16. Then what is the ratio of their circumferences?

56.52:100.48

circumference is the diameter * π

diameter is radius * 2

first circle - >

r = 9

d = 9 * 2 = 18

c = 18 * π ≈ 56.52

second circle - >

r = 16

d = 16 * 2 = 32

c = 32 * π ≈ 100.48

so the ratio of circurfremce for 2 circles that have a ratio of radii 9:16 would be 56.52:100.48