Subject: General Aptitude · Chapter: Problems on Trains · Exam: 2007 · Marks: · Difficulty:
Two trains are coming from opposite directions with speeds of 75 km/hr and 100 km/hr on two parallel tracks. At some moment the distance between them is 100 km. After T hours, distance between them is again 100 km. T is equal to
(a)1 hr
(b)$1 \frac{1}{7} \mathrm{hr}$
(c)$1 \frac{1}{2} \mathrm{hr}$
(d)2 hrs
Answer
Answer (as printed): B
Explanation
Relative speed $=(75+100) \mathrm{km} / \mathrm{hr}=175 \mathrm{km} / \mathrm{hr}$. Time taken to cover 175 km at relative speed = 1 hr. $$\begin{aligned} \therefore T & =\text { Time taken to cover } 200 \mathrm{km} \\ & =\left(\frac{1}{175} \times 200\right) \mathrm{hr}=\frac{8}{7} \mathrm{hr}=1 \frac{1}{7} \mathrm{hr} \end{aligned}$$