The speed of a boat in still water and the speed of the stream are in the ratio 7 : 2. The upstream speed of the boat is 15 km/hr. What is its downstream speed?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 27 km/hr
Write the two speeds as \(7k\) and \(2k\). Upstream the stream is taken away, downstream it is added.
Boat \(=7k\), stream \(=2k\)
Upstream: \(7k-2k=5k=15\), so \(k=3\)
Boat \(=21\) km/hr, stream \(=6\) km/hr
Downstream speed \(=21+6=27\) km/hr