Peter traveled the entire 50 miles trip. If he did the first 12 miles of at a constant rate 36 miles per hour and the remaining trip of at a constant rate 48 miles per hour, what is the his average speed, in miles per hour?	Options:
A) 20mph B) 24mph C) 30mph D) 38mph E) 40mph
Average speed=sum of distance/sum of time. If he travelled the first 12 miles at 36 miles/hr, it would take 0.3 hr. For the remaining trip, if he went at 48 miles/1hr, it would take 1 hour. Then, the average speed is 50miles/(0.3+1)hrs=38miles/1hr.   Therefore, the answer is 38mph.
<result>D</result>
Peter traveled the entire 50 miles trip. If he did the first 12 miles of at a constant rate 36 miles per hour and the remaining trip of at a constant rate 48 miles per hour, what is the his average speed, in miles per hour?