trains

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[email protected]: Senior | Next Rank: 100 Posts; Posts: 30; Joined: Sun Jun 27, 2010 7:55 pm

by [email protected] » Sun Jun 27, 2010 8:04 pm

Two trains are 2 kms apart. Speed of one train is 20m/s and the other train is running at 30 m/s .Lengths of the
trains are 200 and 300m. In how much time do the trains cross each other?

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Source: Beat The GMAT — Problem Solving | Sun Jun 27, 2010 8:04 pm

kvcpk: Legendary Member; Posts: 1893; Joined: Sun May 30, 2010 11:48 pmFollowed by: 7 members; Thanked: 215 times

by kvcpk » Sun Jun 27, 2010 9:47 pm

[email protected] wrote:Two trains are 2 kms apart. Speed of one train is 20m/s and the other train is running at 30 m/s .Lengths of the
trains are 200 and 300m. In how much time do the trains cross each other?

In what directions are the trains running?

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amising6: Master | Next Rank: 500 Posts; Posts: 294; Joined: Wed May 05, 2010 4:01 am; Location: india; Thanked: 57 times

by amising6 » Sun Jun 27, 2010 11:47 pm

[email protected] wrote:Two trains are 2 kms apart. Speed of one train is 20m/s and the other train is running at 30 m/s .Lengths of the
trains are 200 and 300m. In how much time do the trains cross each other?

distance to be covered by train which will overtake is distance between train+length of the train (to be overtaken)=2000+200=2200 m assuming they are travelling in same direction so only car travelling at higher speed will overtake train travelling at 20 m/s
relative speed=30-20=10 m/sec(distance travelled by train at 30 m/sec)every sec
time=distance/speed
time=2200/10=220 sec

if travelling in oipposite direction speed=20+30=50m/sec
time=2200/50=44 sec (tie taken by train travelling at 30 m/sec)
time=2000+300=2300/50=46 sec(time taken by train travelling at 20 m/sec)

Ideation without execution is delusion

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gmatmachoman: Legendary Member; Posts: 2326; Joined: Mon Jul 28, 2008 3:54 amFollowed by: 2 members; Thanked: 173 times; GMAT Score:710

by gmatmachoman » Mon Jun 28, 2010 12:02 am

kvcpk wrote:
[email protected] wrote:Two trains are 2 kms apart. Speed of one train is 20m/s and the other train is running at 30 m/s .Lengths of the
trains are 200 and 300m. In how much time do the trains cross each other?
In what directions are the trains running?

Probably it's a DS question..pick E!!LOL

R&D on GMAT algorithm:

https://www.beatthegmat.com/r-d-on-gmat- ... tml#305739

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kvcpk: Legendary Member; Posts: 1893; Joined: Sun May 30, 2010 11:48 pmFollowed by: 7 members; Thanked: 215 times

by kvcpk » Mon Jun 28, 2010 7:46 am

gmatmachoman wrote:
kvcpk wrote:
[email protected] wrote:Two trains are 2 kms apart. Speed of one train is 20m/s and the other train is running at 30 m/s .Lengths of the
trains are 200 and 300m. In how much time do the trains cross each other?
In what directions are the trains running?
Probably it's a DS question..pick E!!LOL

LOL

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