A) 120 min
B) 160mm
C) 200 min
D) None of these
Correct Answer: B
Solution :
Let \[{{v}_{1}}\] be the velocity of boat in still water Then \[{{v}_{1}}=\frac{8+8}{2}=8\,\,km/hr\] Velocity of water,\[{{v}_{2}}=4\,\,mk/hr\] Time taken for going upstream and back, \[t=\frac{8}{{{v}_{1}}-{{v}_{2}}}+\frac{8}{{{v}_{1}}-{{v}_{2}}}\] \[=\frac{8}{8-4}+\frac{8}{8+4}\] \[=\frac{8}{3}hrs=\frac{8}{3}\times 60\] \[=\mathbf{160}\,\,\mathbf{min}\]
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