Question : A boat covers a distance of 80 km downstream in 8 hours, while it takes 10 hours to cover the same distance upstream. What is the speed (in km/hr) of the boat in still water?
Option 1: 18
Option 2: 12
Option 3: 9
Option 4: 16
Correct Answer: 9
Solution :
Given: A boat covers a distance of 80 km downstream in 8 hours.
Let the boat speed in still water be B.
The speed of water is W.
Then, the downstream speed is (B + W) and the upstream speed is (B – W).
(B + W) × 8 = 80
⇒ (B + W) = 10 ------------------(1)
The boat covers a distance of 80km upstream in 10 hr.
(B – W) × 10 = 80
⇒ (B – W) = 8 -------------------(2)
Solving equation (1) and equation (2), we get,
B = 9 km/hr and W = 1 km/hr
Hence, the correct answer is 9.
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