hr) is-

11
21.5
32
42.5

Answer:- 1

Explanation:-

Solution:

\begin{aligned} Speed of man in still water , \\ x = \frac{9}{2} k m / h r \\ let speed of stream  = y k m / h \\ Downstream speed  = (\frac{9}{2} + y) \\ Upstream speed  = (\frac{9}{2} - y) \\ Accroding to questions, \\ 2 \times [\frac{Distance}{(\frac{9}{2} + y)}] = \frac{Distance}{(\frac{9}{2} - y)} \\ \Rightarrow \frac{2}{\frac{9}{2} + y} = \frac{1}{\frac{9}{2} - y} \\ \Rightarrow \frac{2 \times 2}{9 + 2 y} = \frac{2}{9 - 2 y} \\ \Rightarrow \frac{2}{9 + 2 y} = \frac{2}{9 - 2 y} \\ \Rightarrow 18 - 4 y = 9 + 2 y \\ \Rightarrow 6 y = 9 \\ \Rightarrow y = \frac{9}{6} = \frac{3}{2} = 1.5 k m / h \end{aligned}

$\eqalign{ & {\text{Speed of man in still water , }} \cr & x{\text{ }} = {\text{ }}\frac{9}{2}km/hr{\text{ }} \cr & {\text{let speed of stream = }}y{\text{ }}km/h \cr & {\text{Downstream speed = }}\left( {\frac{9}{2} + y} \right) \cr & {\text{Upstream speed = }}\left( {\frac{9}{2} - y} \right) \cr & {\text{Accroding to questions,}} \cr & {\text{2}} \times \left[ {\frac{{{\text{Distance}}}}{{\left( {\frac{9}{2} + y} \right)}}} \right] = \frac{{{\text{Distance}}}}{{\left( {\frac{9}{2} - y} \right)}} \cr & \Rightarrow \frac{2}{{\frac{9}{2} + y}} = \frac{1}{{\frac{9}{2} - y}} \cr & \Rightarrow \frac{{2 \times 2}}{{9 + 2y}} = \frac{2}{{9 - 2y}} \cr & \Rightarrow \frac{2}{{9 + 2y}} = \frac{2}{{9 - 2y}} \cr & \Rightarrow 18 - 4y = 9 + 2y \cr & \Rightarrow 6y = 9 \cr & \Rightarrow y = \frac{9}{6} = \frac{3}{2} = 1.5\,km/h \cr}$