Explain how?... im learning on my own!

Question

Mom’s car drove 72 miles in 90 minutes. There are 5,280 feet per mile. How fast did she drive in feet per second?

Answer 1

It is much easier to see the answer to this if you write traditional fractions:

72 miles 5280 feet 1 min

---------- * ------------- * --------

90 min 1 mile 60 sec

You see tht the units cancel and then the answer is 72 * 5280/(90 * 60) feet/sec