A train P running at the speed of 80km/h crosses another train Q running at 70 km/h in opposite direction in 18 seconds.  If the length of Q is 150% that of P, then what is the length of P?

300 m

Relative speed = 80 + 70 = 150 km/h = 150 × \(\frac{5}{18}\) m/sec

Total distance covered =  150 × \(\frac{5}{18}\) × 18 = 750 m

Length of trains:

P :  Q = 2 : 3           (150% = \(\frac{150}{100}\) = \(\frac{3}{2}\) )

Total distance = 5R

5R = 750

1R = 150

⇒ Length of P = 2R = 300 m