Two guns were fired from the same place at an interval of 26 min. A person in a train approaching the place hears the 2nd report 25 min later than 1st. Find the speed of the train (in km/hr), supposing that sound travels at 625 m/sec.

90 km/hr

The distance travelled by sound in 1 min. is equal to the distance travelled by man in  train in 25 mins.

              Sound   :   Train

Time           1      :     25

Speed        25     :      1

                  ↓              ↓

                ×25          ×25

                  ↓              ↓

                625          25 m/sec

Speed of train = 25 m/sec = 25 × \(\frac{18}{5}\) = 90 km/h