Subject: General Aptitude · Chapter: Time and Distance · Exam: 2010 · Marks: · Difficulty:
A car takes 15 minutes less to cover a distance of 75 km, if it increases its speed by 10 km/hr from its usual speed. How much time would it take to cover a distance of 300 km using this speed?
(a)5 hours
(b)$5 \frac{1}{2}$ hours
(c)6 hours
(d)$6 \frac{1}{2}$ hours
Answer
Answer (as printed): A
Explanation
Let the usual speed be $x \mathrm{km} / \mathrm{hr}$. Then, $\frac{75}{x}-\frac{75}{x+10}=\frac{15}{60} \Leftrightarrow x(x+10)=3000$ $$\begin{aligned} & \Leftrightarrow x^{2}+10 x-3000=0 \Leftrightarrow(x+60)(x-50)=0 \Leftrightarrow x=50 . \\ & \therefore \text { Required time }=\left(\frac{300}{60}\right) \text { hrs }=5 \text { hrs. } \end{aligned}$$