Question

A salior goes 8 km down stream in 2/3 hours and return back in 60 minutes. find the speed of boat and speed of stream

Answer 1

Let the speed of sailor in still water is x km/hr and the speed of stream is y km/hr.

Now, the speed of boat (upstream) = (x - y) km/hr

and the speed of boat (downstream) = (x + y) km/hr

Now, according to question,

     8/(x + y) = 40/60          {Since time = distance/speed}

=> 8/(x + y) = 4/6

=> 4(x + y) = 8*6

=> 4(x + y) = 48

=> x + y = 48/4

=> x + y = 12   ................1

Again, 8/(x - y) = 1

x - y = 8  ...............2

Add equation 1 and 2, we get

    2x = 20

=> x = 20/2

=> x = 10

From equation 1, we get

     10 + y = 12

=> y = 12 - 10

=> y = 2

Hence, the speed of sailor in still water is 10 km/hr and the speed of stream is 2 km/hr

Answer 2

☆hey friend!!! ☆

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here is your answer ☞
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$first \: \frac{2}{3} \: hr \: = \: 40 \: minutes \\ \\ lets \: the \: speed \: of \: the \: salior \: in \: still \: water \: is \: = \: x \: \frac{km}{hr} \\ \\ and \: the \: speed \: of \: stream \: is \: = \: y \: \frac{km}{hr} \\ \\ now \: the \: speed \: of \: boat \: (upstrem) \: = (x - y) \: \frac{km}{hr} \\ \\ and \: the \: speed \: of \: boat \:(dowmstream) = \: (x + y) \: \frac{km}{hr} \\ \\ now \: \: according \: to \: question \: \\ \\ \ = > \: \frac{8}{x + y} \: = \: \frac{40}{60} .....(since \: time \: = \: \frac{distance}{speed} ) \\ \\ = > \: x + y \: = \: 12...........eq_{1} \\ \\ = > \: again \\ \\ = > \: \frac{8}{x - y} = \: 1 \\ \\ = > \: x - y \: = \: 8 \: .............eq _{2} \\ \\ add \: equation \: 1 \: and \: 2 \: we \: get \\ \\ = > \: 2x \: = \: 20 \\ \\ = > \: x \: = \: 10 \\ \\ from \: equation \: we \: get \: \\ \\ = > \: 10 + y = 12 \\ \\ = > \: y \: = \: 2$


Hence, the speed of sailor in still water is 10 km/hr and the speed of stream is 2 km/hr

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hope it will help you ☺☺☺☺
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Devil_king ▄︻̷̿┻̿═━一