Two gun were fired from the same place at an interval of 13 min. A person in a train approaching the place hears the 2nd report 12 min 30 sec later than 1st. Find the speed of the train (in km/hr), supposing that sound travels at 375 m/sec.

54 km/hr

(Distance covered by bullet in 30 seconds is equal to the distance covered by train in 12 mins 30 seconds)

                  Train            :         Sound

Time     12 min 30 sec     :          30 sec

                     750           :           30

                       25           :            1

Speed                1           :           25

                         ↓                         ↓

                      ×15                     ×15

                         ↓                         ↓

                     15m/sec                375

Speed of train = 15m/sec = 15 × \(\frac{18}{5}\) = 54 km/h