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A train moves past a telegraph post and a bridge 264 m long in 8 seconds and 20 seconds respectively. What is the speed of the train

69.5 km/hr
70 km/hr
79 km/hr
79.2 km/hr
Explanation:

Let the length of the train be $ x $ metres and its speed by $ y $ m/sec.

Then,$ \dfrac{x}{y} $= 8     $\Rightarrow x = 8 y $
Now,$ \dfrac{x + 264}{20} $= $ y $

$\Rightarrow 8 y $ + 264 = 20$ y $

$\Rightarrow y $ = 22.

$\therefore Speed = 22 m/sec$ =$ \left(22 \times\dfrac{18}{5} \right) $km/hr = 79.2 km/hr.
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