Maths question?

Robert B: Maths question?
Suppose train A and train B are travelling towards each other at 40km/h and 50km/h respectively.

When they are 100km apart, a fly which is on the front of train A starts flying towards train B at 90km/h. When it hits train B, it immediately starts flying back towards train A, and when it hits train A it starts flying back towards train B. It keeps flying back and forth between the trains until the trains collide.

How far does the fly travel in total?

Answers and Views:

Answer by Rec
when the fly hits train B, given that it immediately fly back to train A, it’s pretty the same thing that the fly keep flying instead of turning back.

first find how long it takes both train to meet
100 = 40t + 50t
100 = 90t
t = 10/9 hr

the fly will fly back and forth for 10/9hrs
the total distance the fly covers is 90 * 10/9 = 100km <== ans

Answer by Bing
The speed the fly is exactly equal to the combined speed of the two trains. So the distance that the fly flies would we the same as the distance the two trains cover. The two trains will collide at the combined distance of 100km and so, the fly flies at that distance.