Question

a motarboat covers a certain distance downstream in five hours .It covers the same distance upstream in five and a half.the speed of stream is 1.5 km/ h. Find the speed of motarbaot im still water.

Answer 1

let the speed of motorboat be X km/h,
so the speed upstream will be (x-1.5)km/h,
and the speed downstream will be (x+1.5)km/h,

Let the distance covered be Y km,

Time taken = Distance/Speed

Time Upstream= 5.5 = y/(x-1.5)
Time Downstream = 5 =y/(x+1.5)----Eq.2

For Eq.1; 5.5(x-1.5) = y --- Eq.1

From Eq.2,
$5 = \frac{y}{(x + 1.5)}$
$5(x + 1.5) = y$
$5(x + 1.5) = 5.5(x - 1.5)$ [From Eq.1]
$x + 1.5 = 1.1x - 1.65$
$0.1x = 3.15$
$x = 31.5$
So the speed of the motarboat in still water is 31.5 km/h..!!!
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