Question

A boat can be rowed 9 km. upstream or
18 km. downstream in a period of 3 hrs. What is the
speed of the boat in still water in km/hr?​

Answer 1

A boat can be rowed 9 km. upstream or 18 km downstream in a period of 3 hrs. The speed of the boat in still water is 4.5 km/hr

Explanation:

Let the speed of the boat in still water be v km/h and the speed of the river be u km/h

Then

Speed of the boat downstream = (v + u) km/h

Speed of the boat upstream = (v - u) km/h

According to the question

$3=\frac{18}{v+u}$

$\implies v+u=6$  .......... (1)

Again

$3=\frac{9}{v-u}$

$\implies v-u=3$  .......... (2)

Adding eq (1) and eq (2), we get

$2v=9$

$\implies v=4.5$ km/h

Hope this answer is helpful.

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