Joe rode at the speed of 45km per hour from A to B. He then rode back from B to A at the sped of 55km per hour. What is the average speed for the whole trip?

Question

lgbasallote · Answer

isnt it$$\frac{45 + 55}{2}?$$

anonymous · Answer

I originally thought is was but apparently the answer is 49.5km per hour. I would like to know how that answer was obtained.

anonymous · Answer

yu have to use 2v1v2/(v1+v2) i guess

anonymous · Answer

start by takin distance as S
total distance=2*S
total time is s/55 + s/45
simpify

lgbasallote · Answer

ahh yes total time

anonymous · Answer

@shirleyx ,first consider the distance from A to B to be x,time taken to move form A to B be x/45 and from B to A be x/55. average speed is total distance/total time,if you simplify you'll get 49.5

anonymous · Answer

By the way, you can take a mean of velocities, as @lgbasallote thought, but you need to use harmonic, not arithmetic one.

anonymous · Answer

I'm sorry, i still don't get it. what exactly is the equation i need to use?

anonymous · Answer

assume the distance to be equal to 'd' 
the avg speed is given by total distance traveled divided by total time taken
ie. 2d is the total distance and total time taken id d/45 + d/55
therefore avg speed is 2d/d(1/45 + 1/55) 
and there's your answer.