Two trains of equal lengths take 10 seconds and 15 seconds respectively to cross a telegraph post. If the… · ABC26GN3903
Subject: General Aptitude · Chapter: Problems on Trains · Exam: S.S.C. 2004
Two trains of equal lengths take 10 seconds and 15 seconds respectively to cross a telegraph post. If the length of each train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction?
(a)10
(b)12
(c)15
(d)20
Answer
Answer (as printed): B
Explanation
Speed of the first $\operatorname{train}=\left(\frac{120}{10}\right) \mathrm{m} / \mathrm{sec}=12 \mathrm{m} / \mathrm{sec}$. Speed of the second train $=\left(\frac{120}{15}\right) \mathrm{m} / \mathrm{sec}=8 \mathrm{m} / \mathrm{sec}$. Relative speed $=(12+8) \mathrm{m} / \mathrm{sec}=20 \mathrm{m} / \mathrm{sec}$. $$\text { ∴ } \text { Required time }=\frac{(120+120)}{20} \mathrm{sec}=12 \mathrm{sec} .$$