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ACT® Math

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Moderate

Circle Circumference

ACTMAT-GKENY3

Blowing air into a spherical ball caused the circumference of the ball to increase from 12 inches to 16 inches.

By how many inches, then, did the radius increase?

A

$4$

B

$2$

C

$ {\cfrac { 2 }{ \pi } }​ $

D

$ \cfrac{4}{\pi} $

E

$ 2{\pi} $