Ling lives 2 miles from school. It took him 15 minutes to bike from school to home. The first half of the distance he biked at a speed of 12 mph. What was his speed for the remaining distance? What was his average speed?

A) time = distance/speed

For the first half of the trip, the time used was

... (1 mi) / (12 mi/h) = (1/12) h = 5 minutes

Then the last half of the trip took 10 minutes, 1/6 hour.

... speed = distance/time

... = (1 mi) / (1/6 h) = 6 mi/h

The speed for the last half of the trip was 6 mph.

b) The average speed was

... (2 mi) / (1/4 h) = 8 mi/h

Ling's average speed was 8 mph.