Answer:
d. Mom drove at a rate of 70.4 feet per second
Step-by-step explanation:
This is a problem of proportions.
Mom drove 72 miles over a span of 90 minutes
(72 miles) / (90 minutes)
If there are 5,280 feet in a mile, and 60 seconds in a minute, we can solve for her speed in feet per second by multiplying ratios
( 72 miles) / (90 minutes) * (5,280 feet) / (1 mile) * (1 minute) / (60 seconds)
Our numerator is then
(72 miles * 5,280 feet * 1 minute) = 380,160 miles*feet*minute
Our denominator is then
(90 minutes * 1 mile * 60 seconds) = (5,400 minutes*miles*seconds)
Giving us
(380,160 miles*feet*minutes) / (5,400 minutes*miles*seconds)
380,160 / 5,400 = 70.4
Miles and minutes cancel out, leaving us with units
feet / second
So
Mom drove at a rate of 70.4 feet per second
