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?
Accepted Solution
A:
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.Β 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).