Question
A boat can travel 18 km more in downstream than that in
upstream, in 9 hours while the difference between the time taken by the same boat to travel 200 km and 100 km, in still water, is 5 hours. Find the approximate time taken by the boat to travel 250 km in downstream and 200 km in upstream.Solution
Let the speed of boat in still water and speed of stream be 'x' km/hr and 'y' km/hr, respectively. According to question; (200/x) - (100/x) = 5 Or, (100/x) = 5 So, x = 20 Now, 9 x (20 + y) = 9 x (20 - y) + 18 Or, 180 + 9y = 180 - 9y + 18 Or, 18y = 18 So, y = 1 So, downstream speed of the boat = (20 + 1) = 21 km/hr And, upstream speed of the boat = (20 - 1) = 19 km/hr Required time taken = (250/21) + (250/19) ~ (12 + 10) ~ 22 hours
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