Answer: 2.5 hr

Explanation:
let the speed of the train be s kmph, the train approaches the man at
=> The relative speed of (s – 4) kmph
=> (300/1000)[1/(s + 5)] = 30 / 3600
=> s = 40 kmph
=> the distance to the station is 40(15/60) = 10 km
=> the man reaches the station in 10/4 = 2.5 hr

Answer: 70 sec

Explanation:
The distance to be travelled by the train to cross a platform of length
=>750 m is 750 + 650 i.e. 1400 m. At 72 km/hr, or 20 m/s of the train takes 1400/20 i.e. 70 seconds to cross the platform.

Answer: 1000 m

Explanation:
Required distance = Sum of the lengths of the trains = 1000 m

Answer: 72

Explanation:
Speed of the train
=> Length of the train / time taken to cross the pole = 500/25
=> 20 m/sec = 72

Answer: 15, 10

Explanation:
let the speeds of the trains be x m/sec and y m/sec where x>y
=> 300 + 200 / x – y = 100
=> 5 = x - y => (1)
=> 300 + 200 / x + y = 20
=> 25 = x + y =>(2)
=> x = 15 and y = 10

Answer: 600 m

Explanation:
let the length and the speed of the train be l m
=> And s kmph respectively.
=> l = 40(s – 9)5/18 = 48(s – 18)5/18
=> s-9 / s-18 = 48/40
=> s = 63
l = 40(63 – 9) x 5/18 = 600 m

Answer: 30

Explanation:
108 kmph = (108 * 5/18) m/sec = 30 m/sec

Answer: 50.4 kmph    

Explanation:
14 m/sec = (14 * 18/5) = 50.4 kmph

Answer: 2.5 sec   

Explanation:
Speed = (144 * 5/18) = 40 m/sec
Time taken = 100/40 = 2.5 sec

Answer: 16 sec   

Explanation:
Speed = (63 * 5/18) m/sec = 35/2 m/ sec
Time taken = (280 * 2/35) sec = 16 sec