Question 60

A boat goes 2 km upstream and 3 km downstream in 45 minutes while it goes 3 km upstream and 9 km downstream in 90 minutes. What is the speed (in km/hr) of boat when going down stream?

Solution

Let speed of boat going downstream = $$x$$ km/hr and going upstream = $$y$$ km/hr

According to ques,

=> $$\frac{2}{y}+\frac{3}{x}=\frac{3}{4}$$ --------------(i)

Also, $$\frac{3}{y}+\frac{9}{x}=\frac{3}{2}$$ ------------(ii)

Solving above equations, we get : $$y=4$$ and $$x=12$$

$$\therefore$$ Speed (in km/hr) of boat when going down stream = 12

=> Ans - (C)

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