Question

A boat covers the distance between two ports in 6 hours while going down the stream. While going up the stream, it covers the same distance in 9 hours. If the speed of the stream is 2.5km/h, find the speed of the boat in still water.​

Answer 1

Answer:

Let the distance between two port be ′x′ km.

And speed of boat in still water be ′S′ km/hr.

According to question,

In downstream,

x=(S+2)x4   ........(1)                               as,  (Distance= Speed x Time)

Similarly,

In upstream,

v

x=(S−2)x5   ........(2) 

From (1)  & (2),

(S+2)4=(S−2)5

=> 4S+8=5S−10

=> S=18 km/hr.

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Answer 2

Step-by-step explanation:

Let x be the distance

Here 'S' Speed of boat in still water

Speed of stream =2.5Km/hr

Speed in downstream =S+2.5

Time =6hr

Speed =distance /time

x=(S+2.5)*6

x=6S+15 (eqn1)

Speed in upstream =S-2.5

Time =9hr

x=(S-2.5)*9

x=9S-22.5(eqn2)

Equating eqn1 & eqn2 we get

6S+15=9S-22.5

9S-6S=15+22.5

3S=37.5

S=37.5/3

S=12.5

Speed in still water =12.5KM/hr

X=(12.5+2.5)*6=90KM