A 640 metre long train travelling at 80 km/h overtook a 540 metre long train travelling at 72 km/h in the same direction. How long did it take the faster train to cross the other train completely?

8 minutes 51 seconds

Relative spped , when moves in same direction = 80 - 72 = 8 km/h

8 km/h = 8 × \(\frac{5 }{18 }\)m/sec  =  \(\frac{20 }{9}\) m/sec

Total distance = 640 + 540 = 1180 m

Time taken =  \(\frac{1180 × 9  }{20  }\) 

= 531 sec

= 8 minutes 51 seconds