06/18/2020 (2011: Countdown Round, Problem 3)

Q: By how many feet does the circumference of a circle increase if the radius is increased by 20 feet? Express your answer in terms of π.

A: 40π

If the radius is x, then the circumference is 2πx, and then it's increased by 20 feet, then the new circumference is 2πx + 40π.

The circumference increases from 2πx to 2πx + 40π. That means that it increases by 40π.