Subject: General Aptitude · Chapter: Time and Distance · Exam: 2010 · Marks: · Difficulty:
A train travels a distance of 600 km at a constant speed. If the speed of the train is increased by 5 km/hr, the journey would take 4 hours less. Find the speed of the train.
(a)25 km/hr
(b)50 km/hr
(c)100 km/hr
(d)None of these
Answer
Answer (as printed): A
Explanation
Let the speed of the train be $x \mathrm{km} / \mathrm{hr}$. Then, $\frac{600}{x}-\frac{600}{x+5}=4 \Leftrightarrow 4 x(x+5)=3000$ $$\begin{aligned} & \Leftrightarrow 4 x^{2}+20 x-3000=0 \Leftrightarrow x^{2}+5 x-750=0 \\ & \Leftrightarrow(x+30)(x-25)=0 \Leftrightarrow x=25 . \\ & \therefore \text { Speed of the train }=25 \mathrm{km} / \mathrm{hr} . \end{aligned}$$