Question

Jack biked to his friend house at a speed of 10 mph. When he was returning home it was raining. So he biked much slower - at 6 mph. What was Jack's average speed on the way there and back?

Answer 1

Answer:

  7.5

Step-by-step explanation:

The relation between time, speed, and distance is ...

  time = distance/speed

If distance is "1 round trip", then the time going is ...

  going = 0.5/(10 mi/h) . . . . for 1/2 round trip

and the time coming is ...

  coming = 0.5/(6 mi/h)

Then the average speed for the full round trip is ...

  speed = distance/time

  average speed = 1/(going + coming) = 1/(0.5/10 +0.5/6) mi/h

  = 1/((3+5)/60) mi/h

  = 60/8 mi/h = 7.5 mi/h

Jack's average speed for the round trip was 7.5 mph.