Time and Distance

Level pending

Two trains with their speeds in the ratio 3 : 4 3:4 are going in the opposite directions along parallel tracks. If each train takes 3 3 seconds to cross a telegraph post, then find the time taken by the trains to cross each other completely (in seconds).


The answer is 3.

Shreya R by Shreya R , 21, India

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2 solutions

Shreya R
Mar 18, 2014

The length of the 1st train= 3 x . 3 = 9 x 3x.3=9x .
The length of the second train= 4 x . 3 = 12 x 4x.3=12x . Therefore, the total distance= 21 x 21x . Speed= 4 x + 3 x = 7 x 4x+3x=7x . Therefore time taken= Distance/ speed = 21 x 7 x = 3 \frac { 21x }{ 7x } =\quad 3 seconds

4 Helpful 0 Interesting 0 Brilliant 0 Confused
Mark Kong
Jun 3, 2014

The trains start with their heads at the same point. Imagine that there was a telephone post right where they meet. They both take 3 seconds to cross it, so after 3 seconds, both ends of the trains would be there.

1 Helpful 0 Interesting 0 Brilliant 0 Confused

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