The speed of a boat in still water is 15 km/hr and the speed of the stream is 5 km/hr. What distance does the boat travel downstream in 12 minutes?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 4 km
Going downstream, the stream helps the boat, so the two speeds are added. The time must be changed to hours before multiplying by a speed in km/hr.
Downstream speed \(=15+5=20\) km/hr
Time \(\displaystyle =12\text{ min}=\frac{12}{60}=\frac{1}{5}\) hr
Distance \(\displaystyle =20\times\frac{1}{5}=4\) km