A train travels the distance between stations P and Q at a speed of 126 km/h, while in the opposite direction it comes back at 90 km/h. Another train travels the same distance at the average speed of the first train. The time taken by the second train to travel 525 km is:

5 hours

Average Speed = \(\frac{2 × S1 ×S2  }{S1 + S2}\)

= \(\frac{2 × 126 ×90  }{126 + 90}\)

= 105 km/h

Time = \(\frac{Distance }{Speed}\)

= \(\frac{525 }{105}\)

= 5 hours