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

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 = (Distance)/(time)`

As given

18 miles downstream for 3 hours

Now for the downstream

`u + v = (18)/(3)`

u + v = 6

now for the upstream

As given

the trip back against the current takes 6 hours

`u - v = (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