A man swims from A to B and back in 4.5 hours. A block of wood when allowed to go with the stream from A to B takes 6 hours. What is the ratio of the speed of the man in still water to that of the stream?

A. 2 : 1

B. 3 : 1

C. 4 : 1

D. 5: 1

B. 3 : 1

$$
\begin{align}
\frac{d}{b+s}+\frac{d}{b-s} & =\frac{9}{2} \\
\\
\frac{d}{s} & =6
\end{align}
$$

Substituting d = 6s

$$ \frac{6 s}{b+s}+\frac{6 s}{1-s}=\frac{9}{2} $$

Rather than solve, use options –

(A) $\frac{6}{2+1}+\frac{6}{2-1}=8 \neq 9 / 2$.

(B) $\frac{6}{3+1}+\frac{6}{3-1}=4.5$