Subject: General Aptitude · Chapter: Problems on Trains · Exam: · Marks: · Difficulty:
A train takes 5 minutes to cross a telegraphic post. Then the time taken by another train whose length is just double of the first train and moving with same speed to cross a platform of its own length is (Hotel Management, 2007)
(a)10 minutes
(b)15 minutes
(c)20 minutes
(d)Data inadequate
Answer
Answer (as printed): C
Explanation
Let the length of the train be $x$ metres. Time taken to cover $x$ metres $=5 \mathrm{min}$ $$=(5 \times 60) \mathrm{sec}=300 \mathrm{sec} .$$ Speed of the train $=\left(\frac{x}{300}\right) \mathrm{m} / \mathrm{sec}$. Length of the second train $=(2 x)$ metres. Length of the platform $=(2 x)$ metres. $$\begin{aligned} \therefore \text { Required time } & =\left[\frac{2 x+2 x}{\left(\frac{x}{300}\right)}\right] \sec =\left(\frac{4 x \times 300}{x}\right) \mathrm{sec} \\ & =1200 \mathrm{sec}=\left(\frac{1200}{60}\right) \mathrm{min}=20 \mathrm{min} . \end{aligned}$$