When the circumference of a circle is increased from 10 pi inches to 15 pi inches, by how many inche

When the circumference of a circle is increased from 10 pi inches to 15 pi inches, by how many inches is the radius increased?

C = 2pir

Smaller circle:
2pir = 10pi

Divide each side by 2pi:
r = 5

Larger circle:
2pir = 15pi

Divide each side by 2pi:
r = 7.5

Difference = 7.5 - 5 = 2.5 or 2&1/2