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1. Two rifles are fired from the same place at a difference of 11 minutes 45 seconds. But a man who is coming towards the place in a train hears the second sound after 11 minutes. Find the speed of train. (speed of sound = 330 m/s)

A. 72 kmph

B. 36 kmph

C. 81 kmph

D. 108 kmph

Solution:

Distance travelled by man-train in 11 minute = distance traveled by sound in (11 min 45 sec - 11 min) = 45 sec.
Let the speed of train be x kmph.
Now,
Or,

x \times \frac{11}{60} = \frac{45}{3600} \times 330 \times \frac{18}{5}

Or, x = 81 kmph.

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