[quote="gmatmba"][quote="sgrover"]a train crosses a bridge in 5a seconds and crosses anotherr train of length equal to that of the bridge and moving in opp: dirn: in 4a secs.if train overtakes the other train when moving in same direction in 240 secs,what is value of 'a'?
I don't have answer choices but thought it might be an interesting question to solve.[/quote]
Ok here I go:
Let D be the length of the bridge and the second train
S1 = D/5a
S3 = S1 + S2 = D/4a
Therefore, speed of second train (S2) = S3 - S1 = D/20
Also, S2 - S1 = D/240
S1 = D/20 - D/240 = 11D/240
a = 48/11 .... phew!
This question was more Kaplan
-like than Gmat-like. Dont even know if I made a mistake here...please review![/quote]
S2= S3-S1= D/20a
I think we got S1 - S2= D/240
So D/5a - D/20a = D/240 => a=36