The speed of a boat in still water is 5 km/h. If it can travel 26 km downstream and 14 km upstream in the same time, then the speed of the stream is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 1.5 km/h
Downstream the stream adds to the boat’s speed and upstream it takes away from it. The two trips take the same time, so time = distance ÷ speed is equal for both. Let the speed of the stream be \(s\) km/h.
Downstream speed \(=5+s\); upstream speed \(=5-s\)
Equal times: \(\displaystyle\frac{26}{5+s}=\frac{14}{5-s}\)
\(26(5-s)=14(5+s)\)
\(130-26s=70+14s\)
\(40s=60\), so \(s=\) 1.5 km/h