Discussion
If upstream speed is 22 km/hr and downstream speed is 34 km/hr, what is speed of boat in still water?
Answer: A
Write \( b \) for the boat's speed in still water and \( r \) for the stream's. Then
\[ \text{downstream} = b + r, \qquad \text{upstream} = b - r \]
Adding the two eliminates \( r \):
\[ (b + r) + (b - r) = 34 + 22 = 56 \quad\Longrightarrow\quad 2b = 56 \]
\[ b = 28 \text{ km/h} \]
The still-water speed is always the average of the two, and the stream's speed is half their difference: \( r = \tfrac{34-22}{2} = 6 \) km/h. The 56 on offer is the sum, one step short.
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