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A train 100 m long, crosses a man standing nearby in 4 sec. Find its speed in km/hr.

Speed = distance / time

Speed = 100/4 = 25 m/sec

Answer options are given in km/hr. Convert m/sec into km/hr

25 m/sec = (25x3600)/1000 km/hr = 90 km/hr

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A toy train crosses 210 and 122 m long tunnels in 25 and 17 sec respectively. Find the train's length.

Let length of train = x metersSpeed = Distance/TimeFirst distance = 210 + xTime = 25 sec

2nd distance = 122 + xTime = 17 sec

Speed = (210 + x)/25 = (122 + x)/17x = 65 m

2 trains, 100 m and 120 m long are running in the same direction with speeds of 72 km/hr and 54 km/hr. In how much time will the first train cross the second?

Relative speed of trains = 72 - 54 = 18km/hr18km/hr = 5 m/sec

Distance = 100 + 120 = 220 mTime taken = Distance / SpeedTime taken = 220/5 = 44 sec

A 150 m long train crosses a bridge of length 250 m in 30 sec. Find the time the train takes to cross a platform 130 m long.

Distance = 150 + 250 = 400 mSpeed = 400/30 = (40/3) m/sec

Next distance = 150 + 130 = 280 mTime taken = 280/(40/3) = 21 sec