## Microsoft Interview Question Program Managers

- 0of 0 votes
puzzle - 2 trains traveling in opposite direction, bird starts from one and reaches other and flies back and forth like this till train collide. Find the time taken to collide, total distance traveled by the bird, and no. of times bird makes a U turn.

You fool, why won't trains travelling in opposite directions not collide according to the given question.

N plz apply common sense before writing "can never collide".

Everybody know how to find the distance traveled by the bird. The attraction of the question is the second part... The answer will surprise you..... It depends on the size of the bird (If its a point then infinite, if it is not a point then why are we even solving such a puzzle :). BTW for the trains never colliding read: en.wikipedia.org/wiki/Zeno%27s_paradoxes

distance traveled: D/vb, where D is the initial distance and vb is the speed of the bird;

Time U turned: infinite. Suppose finite, at the last U turn, suppose the trains are d apart, in d/(vt + vb) time, the bird run into the other train, however the trains are still d(1 - 2vt/(vt + vb))>0 apart, which means there is another U turn. contradiction

if the time of collision of two trains is finite, how can the number of U turns be infinite??

D: distance between 2 trains

- zglgjg on May 10, 2010 Edit | Flag Replyv1,v2: speeds of two trains

v3: speed of bird(v3>v1 &&v3>v2)

1)Find the time taken to collide

T1=D/(v1+v2)

2)total distance traveled by the bird

D2=T1*v3

3)# of times bird makes a U turn

Maybe infinite (not sure)