Question

Two trains, each having a speed of s, are headed at each other on the same straight track. A bird that can fly at speed 2s flies off the front of one train when they are d apart and heads directly for the other train. On reaching the other train it flies directly back to the first train, and so forth. (We have no idea why a bird would behave in this way.) In terms of variables given in the problem, what is the total distance the bird travels?

Answer 1

The answer is d.

2s(d/s1+s2) = 2s(d/2s) = d