Two trains 110 m and 140 m long are running into same direction on  a parallel track at the speed of 45 km/hr and 25 km/hr respectively . How much long the faster train will take to cross the slower train ( in sec ) ? 

45

Total distance = 110 + 140 = 250 m 

When trains moves in same direction, then relative speed = ( 45 - 25 ) = 20 km/hr

= 20 × \(\frac{5}{18}\) m/sec

Distance = Speed  × Time 

Time taken = \(\frac{250 \;  × \; 18}{20  \; ×\;  5}\)   =  45 sec.