Question

Julie and Eric row their boat (at a constant speed) 18 miles downstream for 3 hours helped by the current. Rowing at the same rate, the trip back against the current takes 6 hours. Find the rate of the boat in still water.

Answer 1

Answer

Find out the the rate of the boat in still water.

To proof

let us assume that the speed of the boat in the still water = u

let us assume that the speed of the current = v

Formula

$speed = \frac{Distance}{time}$

As given

18 miles downstream for 3 hours

Now for the downstream

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

u + v = 6

now for the upstream

As given

the trip back against the current takes 6 hours

$u - v = \frac{18}{6}$

u-v = 3

Than the two equation becomes

u + v = 6 and u - v = 3

add both the above equation

we get

2u = 9

u = 4.5miles per hour

put this in the  u - v = 3

4.5 -v = 3

v =1.5 miles per hour

The rate of  the boat in the still water is  4.5miles per hour .

Hence proved