posted by i love polka .
Mr. Suki plans to drive 900 miles to his farmhouse, driving an average of 50 miles per hour. How many miles per hour faster must he average, while driving to reduce his total driving time by 3 hours?
900 miles at 50 miles an hour will take him 900/50=18 hours. He wants to do it in 15 hours, so he's going to have to travel at 900/15=60 miles an hour. If he does that, he'll have increased his speed by 10 mph.