algebra
posted by susie .
Jim was driving to an interview 72 mi away. On the first leg of the trop he drove an average of 30 mph through a long construction zone, but was able to drive 60 mph after passing through this area. If driving time for the trip was 1 1/2 hr, how long was he driving in the const. zone?

Let the construction zone driving time be T hours. Then, 1.5  T hours were spent driving at 60 mph. The total distance driven is
30*T + 60*(1.5  T) = 72 miles
90  72 = 30 T
T = 0.600 hours = 36 minutes