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  1. A train passes two persons walking in the same direction at a speed of 3 km/hour and 5km/hour respectively in 10 seconds and 11 seconds respectively. The speed of the train is
    1. 28 km/hour
    2. 27 km/hour
    3. 25 km/hour
    4. 24 km/hour
Correct Option: C

Let the speed of train be x kmph and its length be y km.
When the train crosses a man, it covers its own length
According to he question,

=
y
= 10
(x − 3) ×
5
3

⇒  18 y = 10 × 5(x –3)
⇒  18y = 50x –150   ..... (i)
and, 
y
= 11
(x − 5) ×
5
18

⇒  18y = 55(x–5)
⇒  18y = 55x –275   .... (ii)
From equations (i) and (ii),
55x –275 = 50x–150
⇒  55x –50x = 275 – 150
⇒  5x = 125
⇒  x =
125
= 25
5

∴  Speed of the train = 25 kmph
Second Method :
Here, S1 = 3, S2 = 5
t1 =
10
,  t2 =
11
36003600

Speed of train =
t1S1 − t2S2
t1 − t2

=
3 × 10
5 × 11
36003600
10
11
36003600

=
− 25
×
3600
3600− 1

= 25 m/sec



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