Problem: When the circumference of a toy balloon is increased from 20 inches to 25 inches, the radius is increased by:
Answer Choices:
A. 5 in.
B. 221​ in.
C. 5/Ï€ in.
D. 5/2Ï€ in.
E. π/5 in.
Solution:
Since C=2πr, letting r2​ be the original radius, r1​ the final radius, we have 25−20=2πr1​−2πr2​=2π(r1​−r2​);∴r1​−r2​=5/2π.