Question

Dexter needs to drive to a destination 66 miles away. He starts at 2:48pm and needs to arrive at 4:00pm. What speed, in miles per hour, does Dexter need to travel?

Answer 1

`55 mph`

Explanation:

Dexter is going to drive 66 miles and has exactly 72 minutes to get there (there's 12 minutes to get from 2:48pm to 3pm and then another 60 to get to 4pm).

Dexter therefore must drive an average of `(66 " miles")/(72 " minutes")`, or 11 miles every 12 minutes.

We can put this into miles per hour by seeing that we can multiply 12 minutes by 5 to get 60 minutes, which is one hour. And so we do the same for the miles:

`(11 " miles")/(12 " minutes")(5/5)=(55 " miles")/(60 " minutes")=(55 " miles")/(1 " hour")=55 mph`