Question

The amount of time it takes to fill a whirlpool tub is inversely proportional to the square of the radius of the pipe used to fill it. If a pipe of radius 1.5 inches can fill the tub in 8 ​minutes, how long will it take the tub to fill if a pipe of radius 3.5 inches is​ used?

Answer 1

$T= \frac{k}{r^{2}}$
$8= \frac{k}{1.5^{2}}$
$k=8\times(2.25)=18$
$T= \frac{18}{3.5^{2}}=1.47min$