Question

Suppose a tank in Oklahoma City leaks toxic chemicals. The area affected is a circle centered on the tank. When the spill is first noticed, the circle has a radius of 50 feet. A response team arrives 80 minutes later, by which time the affected area has grown to a circle with a radius of 70 feet.

Required:
How rapidly was the radius of the spill changing in ft/min between the time the spill was noticed and the arrival of the response team?

Answer 1

0.5 ft per min

Explanation:

in 80 minutes the radius expanded by 40%

we can set up a proportion of percent change over minutes:

.4/80 = r/1

cross-multiply to get:

80r = .4

r = .005 or 1/2 of a foot per minute