A boat can go 30 km downstream and 24 km upstream in 2 hours 27 mins. Also it can go 10 km downstream and 4 km upstream in 37 mins. What is the speed of the boat upstream (in km/hr)?
Answer & explanation
Correct answer: option 3
Let speed of Boat in still water = u km/hr
speed of stream = v km/hr
ATQ,
⇒ \(\frac{30}{u\;+\;v}\) + \(\frac{24}{u\;-\;v}\) = 147 min ....(i)
⇒ \(\frac{10}{u\;+\;v}\) + \(\frac{4}{u\;-\;v}\) = 37 min ....(ii)
multiply ii by 3 and subtract from (i)
We get,
\(\frac{12}{u\;-\;v}\) = 36 min = \(\frac{36}{60}\) hrs
⇒ (u - v) = \(\frac{12\;×\;60}{36}\) = 20 km/hr