posted by JK on .
Nico drives from school to the store at 25 miles per hour. He drives back to the school (along the same route) at 35 miles per hour, and the returns to the store (via the same route) travelling at 40 miles per hour. Find the average rate for the three trips. Round your answer to the nearest mile per hour.
I know the answer isn't 25+35+40/3=33mph.
Why isn't that the answer?