A man traveled to his country home, a distance of 150 miles, and then back. His average rate of speed going was 50 miles an hour and his average return speed was 30 miles an hour. His average rate of speed for the entire trip was

calculate the time it took him to drive:

he drove 150 miles at 50 mph

150/50 = 3 hrs

150 miles at 30 mph = 150/30=5 hrs

so he drove a total of 5+3 = 8 hours

he drove a total of 150 + 150 = 300 miles

300/8 = 37.5 miles per hour average for entire trip