time speed dist

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mitaliisrani: Senior | Next Rank: 100 Posts; Posts: 56; Joined: Sun Mar 21, 2010 11:06 am

by mitaliisrani » Thu Sep 02, 2010 9:55 pm

Two trains T1 T2, which are 539 km apart start at the same time, move towards each other. They just complete crossing each other in 3hrs 20 mins. fIND THE DIFFERENCE BETWEEN THE LENGTHS OF THE TWO TRAINS, GIVEN THAT THEIR LENGTHS ARE IN THE RATIO 2:3 AND THEIR SPEEDS ARE 25M/S and 20m/s respectively
A) 100m
B) 200m
C) 500m
D) 150m

OA is
B

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Source: Beat The GMAT — Problem Solving | Thu Sep 02, 2010 9:55 pm

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Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members; Location: Milpitas, CA; Thanked: 447 times

by Rahul@gurome » Thu Sep 02, 2010 11:03 pm

Solution:
Let the length of the trains be 2x and 3x.

So the distance being covered in 3hrs 20 minutes is 539 + 2x +3x = 539+5x.

Their speeds are 25m/s and 20m/s.
Or relative speed is (25+20) = 45m/s = 162km/hr since the two trains are moving in opposite directions.

So (539+5x)/162 = 3 + 20/60 hrs = 10/3
Or 539 + 5x = 540.
Or x = 1/5 km = 200m.

The correct answer is (B).

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