On a trip covering 250 km, a bicyclist travels the first 100 km at 20 km per hour and the remainder of the distance at 15 km per hour. What is the average speed, in km per hour, for the entire trip?  Choose the most appropriate option:
A) 15.8	B) 16.3	C) 16.7	D) 17.2	E) 17.5

Rationale: "time 1 = 100 / 20 = 5 hours time 2 = 150 / 15 = 10 hours total time = 15 hours average speed = 250 / 15 = 16.7 km / hr the answer is c ."
Answer: C