a) 43.2
b) 48
c) 41.6
d) 44.8

Answer: c
Explanation: Let the speed of the current be x kmph
Then speed of the boat in still water = 5x
$$\eqalign{ & {\text{Downstream speed}} \cr & {\text{ = }}\left( {5x + x} \right) = 6x\,kmph \cr & {\text{Upstream speed}} \cr & {\text{ = }}\left( {5x – x} \right) = 4x\,kmph \cr & {\text{Now, }} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{13}}{\text{.2km}}\,\,\,\, \cr & {\text{A}}\overline {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} {\text{B}} \cr & {\text{According to question,}} \cr & {\text{1}}{\text{.1}} \times {\text{6}}x = 13.2 \cr & \Rightarrow 6.6x = 13.2 \cr & \Rightarrow x = \frac{{13.2}}{{6.6}} \cr & x = 2\,kmph \cr & {\text{Upstream speed}} \cr & {\text{ = 4}}x = 4 \times 2 = 8\,kmph \cr & {\text{312 minutes}}\, \cr & = 5\frac{1}{5}\,hours \cr & = \frac{{26}}{5}\,hours \cr & {\text{Required distance travelled upstream}} \cr & {\text{ = Speed }} \times {\text{Time}} \cr & {\text{ = 8}} \times \frac{{26}}{5} = 41.6\,km \cr} $$