Starting at home, Jessica traveled uphill to the grocery store for 18 minutes at just 20 mph. She then traveled back home along the same path downhill at a speed of 60 mph.What is her average speed for the entire trip from home to the grocery store and back?

Use distance = rate x time

18 minutes is 3/10 of an hour.

So the distance to the store is:
d = 20*(3/10) = 6 miles

The distance downhill is the same, 6 miles. So:
6 = (60)t
6/60 = t
1/10 = t
Where t is the time it took to go back home.  So t is .1 hour (6 minutes).

To calculate average speed we use the formula:

average speed = total distance/ total time
average speed = (6+6)/(.3 + .1) = 12/(.4) = 30

So her average speed for the entire trip is 30 mph (miles per hour).