A) 2 km/h
B) 3 km/h
C) \[\frac{1}{2}\text{km/h}\]
D) 1 km/h
Correct Answer: A
Solution :
| [a] Let the speed of water current = x km/h According to the question, \[\frac{24}{10+x}+\frac{24}{10-x}=5\] \[\Rightarrow \] \[24\,[10-x+10+x]=5\,({{10}^{2}}-{{x}^{2}})\] \[\Rightarrow \] \[100-{{x}^{2}}=\frac{24\times 20}{5}=96\] \[\Rightarrow \] \[{{x}^{2}}=4\]\[\Rightarrow \]\[x=\sqrt{4}=2\,km/h\] |
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