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# a train crosses a bridge in 5a seconds and crosses anotherr

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Senior Manager
Joined: 07 Jul 2005
Posts: 404
Location: Sunnyvale, CA
Followers: 2

Kudos [?]: 4 [0], given: 0

a train crosses a bridge in 5a seconds and crosses anotherr [#permalink]  23 Jun 2006, 15:45
00:00

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(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 1 sessions
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 directio

in 240 secs,what is value of 'a'?

I don't have answer choices but thought it might be an interesting question to solve.
Director
Joined: 16 Aug 2005
Posts: 946
Location: France
Followers: 1

Kudos [?]: 10 [0], given: 0

Re: PS : Train [#permalink]  23 Jun 2006, 19:27
sgrover wrote:
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.

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!
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Manager
Joined: 01 Jun 2006
Posts: 141
Followers: 1

Kudos [?]: 2 [0], given: 0

Re: PS : Train [#permalink]  23 Jun 2006, 20:13
[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
Director
Joined: 06 May 2006
Posts: 780
Followers: 3

Kudos [?]: 17 [0], given: 0

V1 = d/5a
V1+V2=d/4a
V1-V2=d/240

=> (1/4a)-(1/240)=2/5a => a=36
Senior Manager
Joined: 16 Apr 2006
Posts: 280
Followers: 2

Kudos [?]: 56 [0], given: 2

Speed be S1, s2
Length of bridge = L
Time Taken a, 4a

S1*5a = L = (s1+s2)*4a
(s1-s2)*240 = L

S1a = 4a*s2
S1 = 4*S2

3S2*240 = 20as2
a = 36
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