# A train running at 72 km/h crosses a platform in 20 seconds and a post in 5 seconds. Find the ratio of length of the platform and length of train.

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A train running at 72 km/h crosses a platform in 20 seconds and a post in 5 seconds. Find the ratio of length of the platform and length of train.

1. 1 : 3
2. 1 : 2
3. 3 : 1
4. 4 : 1
5. 1 : 5

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Correct Answer - Option 3 : 3 : 1

Given:

Speed of train = 72 km/h

Time taken by train to cross a platform = 20 seconds

Time taken by train to cross a pole = 5 seconds

Formula:

Speed = distance/time

Distance = speed × time

Speed in km/h to m/s = multiply by 5/18

Calculation:

Speed of train in m/s = 72 × 5/18 = 20 m/s

Time taken by train to cross a pole = 5 seconds

Distance covered by train to cross a pole = The length of the train

Distance = 20 × 5 = 100 m

Distance covered in crossing the platform = 20 × 20 = 400m

Length of platform = 400 – 100 = 300 m

Ratio of length of platform to length of train = 300 : 100

The required ratio is 3 : 1