Find the ratio of swimming speed of Vikash in still water to speed of river, if ratio of time taken to go 5 km upstream to time taken to go 5 km downstream is 10 : 5?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 3 : 1
For the same distance, speed and time are in inverse ratio. Let Vikash’s speed in still water be \(b\) and the river’s speed \(s\); upstream he swims at \(b-s\), downstream at \(b+s\).
Time upstream : time downstream \(=10:5=2:1\)
So speed upstream : speed downstream \(=1:2\)
Upstream speed over downstream speed: \(\displaystyle \frac{b-s}{b+s}=\frac{1}{2}\)
\(2b-2s=b+s\), so \(b=3s\)
\(b:s=3:1\)