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A boat covers a certain distance downstream in 1 hour, while it comes back in $$1\frac{1}{2}$$ hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?
Answer & Solution
Correct Answer:
Option
D
Let the speed of the boat in still water be x kmph
Then
Speed downstream = (x + 3) kmph
Speed upstream = (x - 3) kmph
$$\eqalign{ & \therefore \left( {x + 3} \right) \times 1 = \left( {x - 3} \right) \times \frac{3}{2} \cr & \Rightarrow 2x + 6 = 3x - 9 \cr & \Rightarrow x = 15\,\text{kmph} \cr} $$
Then
Speed downstream = (x + 3) kmph
Speed upstream = (x - 3) kmph
$$\eqalign{ & \therefore \left( {x + 3} \right) \times 1 = \left( {x - 3} \right) \times \frac{3}{2} \cr & \Rightarrow 2x + 6 = 3x - 9 \cr & \Rightarrow x = 15\,\text{kmph} \cr} $$
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