If a car went the first third of the distance at 80 kmh, the second third at 15 kmh, and the last third at 48 kmh, what was the average speed of the car for the entire trip?
Choose the correct choice from the following
A) 30 kmh  B) 40 kmh  C) 42 kmh  D) 44 kmh  E) 50 kmh

Rationale: "assume d / 3 = 240 ( this number is convenient because it is divisible by 80 , 15 and 48 ) so : 240 = 80 * t 1 = 3 hrs 240 = 15 * t 2 = 16 hrs 240 = 48 * t 3 = 5 hrs t = t 1 + t 2 + t 3 = 24 hrs d = rt ( 240 * 3 ) = r * 24 r = 30 answer : a"
Answer: A