A boat takes 3 hours to travel from a place A to place B downstream and back from B to A upstream. If the speed of the boat in still water is 4 km/h what is the distance between the two places?
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12 km
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16 km
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18 km
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Data inadequate
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None of these
D
Correct answer
Explanation
We know boat speed = 4 km/h and total time = 3 hours. Let distance = d and stream speed = s. Downstream: time = d/(4+s). Upstream: time = d/(4-s). We have d/(4+s) + d/(4-s) = 3. This is one equation with two unknowns (d and s), so we cannot determine d uniquely. Option D is correct.