Question

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?

Answer 1

The average speed is 40 miles per hour.

Answer 2

Based on the formula
`distance = velocity*time` we can find the distance from the grocery store:


`distance = velocity * time = 20mph * (18)/(60)hrs = 6 miles`

Based on this distance we can find the time it took her to get back using the formula
`time = (distance)/(velocity):`


`time = (distance)/(velocity) = (6 miles)/(60mph) = (1)/(10)hrs = 6 minutes`

After this you just take the average of Jessica going at 20 mph for 18 minutes and 60 mph for 6 minutes:


`(20mph * 18min + 60mph*6min)/(24min) = 30mph`

:)