Sam left his school at 3:05. He walked at a speed of 3.2 mph. 15 minutes later, Al started running after him, and he caught up with Sam 10 minutes later. What was Al’s speed?
Sam has a head start of 3.2 m/hr x 1/4 hr = .8 miles
Al has to cover this .8 miles PLUS the distance Sam covers in an additional 10 minutes
Sam's additional distance in 10 minutes = 3.2 m/hr x 10/60 hr = .5333 mile
So AL has to cover .8 mile + .5333 miles in 10 minutes to catch Sam
(.8mile + .5333 mile) / (10/60 hr) = 8 m/hr