A boat can tavel 10 km upstream and 20 km downstream in 7 hours. It can travel 20 km upstream and 10 km downstream in 11 hours. What is the speed of bout in still water?
Answer & explanation
Correct answer: option 3
Let the speed of the boat = a and speed of the stream = b
Given,
A boat can tavel 10 km upstream and 20 km downstream in 7 hours. It can travel 20 km upstream and 10 km downstream in 11 hours.
According to the question,
\(\frac{10}{a-b}\) + \(\frac{20}{a+b}\) = 7 ----(M)
\(\frac{20}{a-b}\) + \(\frac{10}{a+b}\) = 11 ----(N)
By multiplying equation M with 2 we get,
\(\frac{30}{a+b}\) = 3
a + b = 10-----(k)
By multiplying equation N with 2 we get,
\(\frac{-30}{a-b}\) = 15
a - b = 2-----(l)
So, from k and l
a = 6 km/h