A man rows a boat downstream in 3 hours and returns the same distance upstream in 6 hours. If the speed of the stream is 2 km/hr, then the speed of the boat in still water is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 6 km/hr
Let the speed of the boat in still water be x km/hr. The stream adds to the speed downstream and subtracts from it upstream:
\( \text{downstream speed} = x + 2 \)
\( \text{upstream speed} = x - 2 \)
The distance is the same both ways (distance = speed × time):
\( 3(x + 2) = 6(x - 2) \)
\( 3x + 6 = 6x - 12 \)
\( 3x = 18 \)
\( x = 6 \)
Check: the distance is 3 × 8 = 24 km downstream and 6 × 4 = 24 km upstream.