The upstream speed of a boat is 60% of its downstream speed. The speed of the boat in still water is 16 km/hr. What is the speed of the stream?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 4 km/hr
The speed in still water is the average of the downstream and upstream speeds. Writing the upstream speed as 60% of the downstream speed gives the downstream speed.
Let the downstream speed be \(D\); upstream speed \(=0.6D\)
Speed in still water \(\displaystyle =\frac{D+0.6D}{2}=0.8D=16\), so \(D=20\) km/hr
Upstream speed \(=0.6\times20=12\) km/hr
Speed of the stream \(\displaystyle =\frac{20-12}{2}=4\) km/hr