I drove to my parents' house at 40 miles per hour. If I had driven 30 miles an hour instead, then I would have gotten there 20 minutes later. How many miles did I drive?
rate * time = distance
distance is same so equate:
40 m/hr * x = 30 m/hr (x+1/3) solve for x = 1 hour (be careful....you need to change 20 min into 1/3 hour becuase the other parameters are in miles/hr)
40 m/hr x 1 hr = 40 miles