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A train that is $280$ metres long, travelling at a uniform speed, crosses a platform in $60$ seconds and passes a man standing on the platform in $20$ seconds. What is the length of the platform in metres?

Speed of train$=280/20=14m/s$

Let $L$ be the length of platform

$280+L$  covered in $60s$

$\frac{280+L}{14}=60$

$280+L=840$

$L=840-280$

$L=560m$
For a train to cross a person, it takes 20 seconds for its 280m. so d=s*t  then 280=s*20 then we get s=14m/s and in

60 seconds. Total distance travelled should be 840 bcz  d=14*60 =840. Including 280 train length so length of plates =840-280=560

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