Discussion

The speed of a boat in still water is 60kmph and the speed of the current is 20kmph. Find the speed downstream and upstream?

Answer: B

With \( b \) the still-water speed and \( r \) the stream's,

\[ \text{downstream} = b + r, \qquad \text{upstream} = b - r \]

\[ \text{downstream} = 60 + 20 = 80 \text{ kmph} \]

\[ \text{upstream} = 60 - 20 = 40 \text{ kmph} \]

The two speeds always straddle the still-water speed, one above and one below by the same amount - here 20 kmph either side of 60.

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