posted by Rose .
Mrs. Lewis plans to drive 900 miles to her vacation destination, driving an average 50 miles per hour. How many miles per hour faster must she average, while driving, to reduce her total driving time by 3 hours?
I'm not sure how to set up the equation. Thanks.
distance = rate x time
900 = 50*time
time = 900/50 = 18 hours.
To reduce the time by 3 hours means Mrs. Lewis must drive the 900 miles in 15 hours. Use the above to calculate the rate for 15 hours.