Subject: General Aptitude · Chapter: Problems on Trains · Exam: 2010 · Marks: · Difficulty:
A train 108 m long moving at a speed of 50 km/hr crosses a train 112 m long coming from opposite direction in 6 seconds. The speed of the second train is
(a)48 km/hr
(b)54 km/hr
(c)66 km/hr
(d)82 km/hr
Answer
Answer (as printed): D
Explanation
Let the speed of the second train be $x \mathrm{km} / \mathrm{hr}$. Relative speed $=(x+50) \mathrm{km} / \mathrm{hr}$ $$=\left[(x+50) \times \frac{5}{18}\right] \mathrm{m} / \mathrm{sec}=\left(\frac{250+5 x}{18}\right) \mathrm{m} / \mathrm{sec} .$$ Distance covered $=(108+112)=220 \mathrm{m}$. $$\therefore \frac{220}{\left(\frac{250+5 x}{18}\right)}=6 \Leftrightarrow 250+5 x=660 \Leftrightarrow x=82 \mathrm{km} / \mathrm{hr} .$$