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Standard XII

Mathematics

Permutation

Two trains wi...

Question

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

3

sec

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4

sec

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7

sec

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21

sec

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Solution

The correct option is A $3$ sec
Length of Ist train $= 3 x \times .3 = 9 x$
Length of IInd train $= 4 x \times 3 = 12 x$
Total distance $= 21 x$
Speed $= 4 x + 3 x = 7 x$
$∴$ time $= \frac{21 x}{7 x} = 3 s e c$

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

The correct option is A 3 secLength of Ist train =3x×.3=9xLength of IInd train =4x×3=12xTotal distance =21xSpeed =4x+3x=7x∴ time=21x7x=3sec

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

The correct option is A $3$ sec
Length of Ist train $= 3 x \times .3 = 9 x$
Length of IInd train $= 4 x \times 3 = 12 x$
Total distance $= 21 x$
Speed $= 4 x + 3 x = 7 x$
$∴$ time $= \frac{21 x}{7 x} = 3 s e c$