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A man standing on a railway platform noticed that a train took $21\, s$ to cross the platform (this means the time elapsed from the moment the engine enters the platform till the last compartment leaves the platform) which is $88\,m$ long, and that it took $9 s$ to pass him. Assuming that the train was moving with uniform speed, what is the length of the train in meters?
$55$
$60$
$66$
$72$
Solution
(c)
Let the length of trains be $x$ meter.
Time taken by train $h$ cross person $=9\,s$
$\therefore$ Speed of trains $=\frac{x}{9} m / s$
Time taken by train to cross platform $=21\,s$
$\therefore \frac{x}{9}=\frac{x+88}{21}$
${[\because \text { length of plateform }=88\,m ]}$
$\Rightarrow 21 x=9 x+9 \times 88$
$\Rightarrow 12 x=9 \times 88$
$\Rightarrow x=\frac{9 \times 88}{12}=66\,m$