A train speeds past a pole in 15 seconds and a platform 100 m long in 25 seconds. Its length is:
50 m
150 m
200 m
Data inadequate
Explanation:
Let the length of the train be $ x $ metres and its speed by $ y $ m/sec.
| Then,$ \dfrac{x}{y} $= 15 $\Rightarrow$ $ y $ =$ \dfrac{x}{15} $. |
| $\Rightarrow \dfrac{x + 100}{25} $=$ \dfrac{x}{15} $ |
$\Rightarrow 15( x $ + 100) = 25$ x $
$\Rightarrow 15 x $ + 1500 = 25$ x $
$\Rightarrow 1500 = 10 x $
$\Rightarrow x $ = 150 m.