a) 50 m
b) 150 m
c) 200 m
d) Data inadequate
Answer: b
Explanation:
$$\eqalign{
& {\text{Let}}\,{\text{the}}\,{\text{length}}\,{\text{of}}\,{\text{the}}\,{\text{train}}\,{\text{be}}\,x\,{\text{metres}} \cr
& \,{\text{and}}\,{\text{its}}\,{\text{speed}}\,{\text{by}}\,y\,{\text{m/sec}} \cr
& Then,\,\frac{x}{y} = 15\,\,\,\,\,\, \Rightarrow \,\,\,\,\,y = \frac{x}{{15}} \cr
& \frac{{x + 100}}{{25}} = \frac{x}{{15}} \cr
& 15\left( {x + 100} \right) = 25x \cr
& 15x + 1500 = 25x \cr
& 1500 = 10x \cr
& x = 150m \cr} $$.
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