Subject: General Aptitude · Chapter: Boats and Streams · Exam: 2005 · Marks: · Difficulty:
A man rows to a place 48 km distant and back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The rate of the stream is :
(a)1 km/hr
(b)1.5 km / hr
(c)1.8 km / hr
(d)3.5 km / hr
Answer
Answer (as printed): A
Explanation
Suppose he moves 4 km downstream in $x$ hours. Then, Speed downstream $=\left(\frac{4}{x}\right) \mathrm{km} / \mathrm{hr}$. $$\begin{aligned} & =\text { Speed upstream }=\left(\frac{3}{x}\right) \mathrm{km} / \mathrm{hr} . \\ \therefore \quad & \frac{48}{(4 / x)}+\frac{48}{(3 / x)}=14 \text { or } x=\frac{1}{2} . \end{aligned}$$ So, Speed downstream $=7 \mathrm{km} / \mathrm{hr}$, Speed upstream $=6 \mathrm{km} / \mathrm{hr}$ Rate of the stream $=\frac{1}{2}(8-6) \mathrm{km} / \mathrm{hr}=1 \mathrm{km} / \mathrm{hr}$.