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What is the speed of the boat in still water? I. Upstream speed is 4 km/h. II. Downstream speed is 6 km/h.

Difficulty: Easy

Both statements together are necessary
Neither statement alone nor both together are sufficient
Statement II alone is sufficient; Statement I alone is not
Statement I alone is sufficient; Statement II alone is not
None of these

Correct Answer: Both statements together are necessary

Explanation:

Introduction / Context:
Let u be boat speed in still water; v be stream speed. Upstream = u − v; downstream = u + v.

Reasoning:

I: u − v = 4 (two unknowns, one equation) ⇒ insufficient.
II: u + v = 6 ⇒ insufficient alone.
I + II: Solve u = ( (u − v) + (u + v) ) / 2 = (4 + 6)/2 = 5 km/h. Sufficient.

Final Answer:
Both statements together are necessary.

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