alleryA boat’s still-water speed is 12 km/h. It covers 30 km downstream and 18 km upstream in 4 h. Find the positive stream speed.
A3 km/h
B2 km/h
C1 km/h
D4 km/h
Answer & Solution
Correct answer: A. 3 km/h
For stream speed x, 30/(12+x) + 18/(12−x) = 4 reduces to x(x−3)=0; the positive solution is 3 km/h.
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