# A hot air balloon begins its descent at a rate of 221/2 feet per minute. How long will it take for the balloon' s elevation to change by —315 feet?

Nov 8, 2015

It will take 14 minutes for the balloon to descend 315 ft.

#### Explanation:

This question requires knowledge of the Speed formula ($s = \frac{d}{t}$). Where:
s = speed
d = distance
t = time

You are given a speed of -22.5 feet per minute and a distance of -315 feet. If you plug these values in you get the following equation:

$- 22.5 \frac{f t}{\min} = \frac{- 315 f t}{t}$

You then re-arrange the formula to solve for time:

$t = \frac{- 315 f t}{- 22.5 \frac{f t}{\min}}$

When you solve this formula, the feet and negative signs will cancel out leaving positive minutes as your unit. Dividing 315 by 22.5 gives you 14 as your number.