I drove to the beach at a rate of 40 miles per hour. If I had driven at a rate of 36 miles per hour instead, then I would have arrived 20 minutes later. How many miles did I drive?
T ==Time taken to drive to the beach
D / 40 ==T
D / 36 ==T + 20/60, solve for D, T
Use substitution to get:
D==120 miles - distance travelled
T==3 hours - time taken to drive to the each at 40 mph.
120 / 36 ==3 + 1/3 hours -time to get to the beach driving at 36 mph.