Subject: General Aptitude · Chapter: Time and Distance · Exam: · Marks: · Difficulty:
Mary jogs 9 km at a speed of 6 km per hour. At what speed would she need to jog during the next 1.5 hours to have an average of 9 km per hour for the entire jogging session?
(a)9 kmph
(b)10 kmph
(c)12 kmph
(d)14 kmph
Answer
Answer (as printed): C
Explanation
Let speed of jogging be $x \mathrm{km} / \mathrm{hr}$. Total time taken $=\left(\frac{9}{6} \mathrm{hrs}+1.5 \mathrm{hrs}\right)=3 \mathrm{hrs}$. Total distance covered $=(9+1.5 x) \mathrm{km}$. $$\begin{aligned} & \therefore \quad \frac{9+1.5 x}{3}=9 \Leftrightarrow 9+1.5 x=27 \Leftrightarrow \frac{3}{2} x=18 \\ & \Leftrightarrow \quad x=\left(18 \times \frac{2}{3}\right)=12 \mathrm{kmph} . \end{aligned}$$