Question

PLEASE HELP
The current in a nearby river is 5 mph. John wants to be able to travel up the river for a
distance of 30 miles and return to his starting point in a total of 8 hours. How fast must John
be able to row his boat in order to accomplish this? (Assume that the speed that John can
row refers to how fast he can row in still water.)

Answer 1

@dan815 @nincompoop

Answer 2

He travels a total time of 8 hours.
If he travels up the river for t time, how much time will he travel down the river?

Answer 3

i have no idea!! please explain

Answer 4

@mathstudent55

Answer 5

Ok.
The total trip is 8 hours.
time going up + time going down = 8 hours
If you let the time going up be called just t, then you have
t + time going down = 8 hours
Ok so far?

Answer 6

ok

Answer 7

Now let's see if we can get an expression for the time going down.

t + time going down = 8

Subtract t from both sides:

time going down = 8 - t

Now we have:
Time going up = t
Time going down = 8 - t

Ok?

Answer 8

ok

Answer 9

Ok. I put the info we have in the table below.
Now we need the speed going up and the speed going down, and the distances going up and down.

Answer 10

Let's do the distances first bec they are very easy.

Answer 11

How far does he row each way?

Answer 12

like how am i supposed to know im so confused on this question

Answer 13

Have you read the problem?
It's written right there.
There is no calculation needed.

Answer 14

Does this help?

\(\sf John ~wants ~to ~be ~able ~to ~travel ~up ~the ~river ~for ~a ~distance ~of ~\huge \color{red}{30 ~miles}\)
\( \sf and ~return ~to ~his ~starting ~point ~in ~a ~total ~of ~8 ~hours. \)

Answer 15

so for up its 30 ?

Answer 16

Right, Each part of the trip is 30 miles.
We can add the distances to our table.

Answer 17

ok