Home » Aptitude » Speed, Time and Distance » Question
  1. A man standing on a 170 metre long platform watches that a train takes
    7
    1
    seconds to pass him and 21 seconds to cross
    2
    the platform. Find the speed of train.
    1. 12
      16
      m/sec.
      27
    2. 12.5 m/sec.
    3. 12
      13
      m/sec.
      27
    4. None of these
Correct Option: A

Let the length of the train be x m and its speed y m/sec.
Distance covered in crossing the platform = 170 + x metres
and time taken = 21 seconds

∴  Speed y =
170 + x
    ...(i)
21

Distance covered to cross the man = x metres
and time taken = 7
and time taken = 7
1
=
15
seconds
22

∴  Speed y =
x
=
2x
    ...(ii)
15/215

From equations (i) and (ii),
170 + x
=
2x
2115

⇒  2550 + 15x = 42x
⇒  42x – 15x = 2550
⇒  27x = 2550
⇒  x =
2550
= 94
4
metres
279

From equation (ii),
y =
2 × 2550
15 × 27

=
340
= 12
16
m per sec.
2727

Hence, speed = 12
16
m per sec.
27



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