A professor drove from Denver to Boulder during rush hour at an average speed of 30 miles per hour, and then drove back the same way at an average speed of 45 miles per hour.

If the round trip took 1 hour and 45 minutes, how many miles is the professor's one-way trip from Denver to Boulder?

Solution:

The distance is x

x/30+x/45 = 7/4

So

x = 31.5

So the professor's one-way trip from Denver to Boulder is 31.5 miles