man drives for a time at 20 mph. then for a time at 45 mph.he drives 25 mi. he drives 50 min. . how many miles did he drive 20 mph ?
time driven at 20 mph --- x hrs
time driven at 45 mph --- 50/60 - x hrs
20x + 45(50/60 - x) = 25
20x + 37.5- 45x = 25
-25x = -12.5
x = .5 hrs
he drove 30 minutes at 20 mph and 20 min at 45 mph
check: (1/2)(20) + (20/60)(45) = 25