If a car went the first third of the distance at 80 kmh, the second third at 24 kmh, and the last third at 54kmh, what was the average speed of the car for the entire trip? Choose the correct choice from the following choices.
A) 36 kmh  B) 40 kmh  C) 41 kmh  D) 44 kmh  E) 50 kmh

Rationale: "assume d / 3 = 2160 ( this number is convenient because it is divisible by 80 , 24 and 54 ) so : 2160 = 80 * t 1 = 27 hrs 2160 = 24 * t 2 = 90 hrs 2160 = 54 * t 3 = 40 hrs t = t 1 + t 2 + t 3 = 157 hrs d = rt ( 240 * 3 ) = r * 157 r = 41.27 answer : c"
Answer: C