A boatman rows 27 km downstream in 1 hour 30 minutes and 20 km upstream in 2 hours. What is the speed of the stream?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 4 km/hr
The downstream speed is more than the upstream speed by twice the speed of the stream (the stream is added one way and taken away the other way).
Downstream speed \(\displaystyle =\frac{27}{1.5}=18\) km/hr
Upstream speed \(\displaystyle =\frac{20}{2}=10\) km/hr
Speed of the stream \(\displaystyle =\frac{18-10}{2}=4\) km/hr