Question
A boat takes 5 hours longer to travel 15 km upstream
than it does to travel 20 km downstream. The speed of the boat in still water is 5 km/hr. Calculate the speed of the current.Solution
Let the speed of the current be x km/hr According to the question, 15/(5 – x) – 20/(5 + x) = 5 Or, x2 + 7x – 30 = 0 Or, x2 + 10x – 3x – 30 = 0 Or, x(x + 10) – 3(x + 10) = 0 Or, (x – 3) = 0 or, (x + 10) = 0 X = -10 km/hr not possible Therefore, x = 3 km/hr Hence, option b.
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