A car travels at 80mph for 40 miles 72mph for 48miles and th

A car travels at 80mph for 40 miles, 72mph for 48miles, and then 96mph for 32 miles. What is the average rate of speed over the entire trip?

40 miles at 80 mph takes 30 minutes
48 miles at 72 mph takes 40 minutes
32 miles at 96 mph takes 20 minutes
------120 miles in 90 minutes
= 4/3 miles/minute
= 80 mph