math word problem
posted by M.A. .
Here's the latest from the UMW math department: Andy drove from Richmond to Boston at an average speed of 50 miles per hour. If it took 5 hours to drive from Richmond to Philadelphia at an average speed of 70 miles per hour and if the whole trip took 13 hours, how far is it from Philadelphia to Boston?
100 miles
200 miles
300 miles
400 miles
Explain your answer.

Implicit in the question is geography:
All three cities lie on the Interstate highway I95, with Boston in the north, and Richmond (Va) in the south.
Whole trip (Richmond to Boston) took 13 hours, so total distance = 13*50=650 miles
Richmond to Philadelphia=70mph*5 hours=350 miles.
What is the distance between Philadelphia and Boston?