Asked by Tia

A tour boat on a river traveled 40 miles downstream in 4 hours. The return trip against the current took 5 hours. What was the rate of the current?

A. 2.0 MPH
B. 1.5 MPH
Answered by Tia
C. 0.5 MPH
D. 1.0 MPH

I do not get this so it would be great for some help. Thank you!
Answered by Reiny
let the speed of the boat in still waters be x mph
let the speed of the current be y mph
So going downstream or with the current the speed is x+y
going against the current the speed is x-y

so 40/(x+y) = 4
4x + 4y = 40
x + y = 10 , #1
and
40/(x-y) = 5
5x - 5y = 40
x-y = 8 , #2

add#1 and #2
2x = 13
x = 6.5
in #1
6.5 + y = 10
y = 3/5

Therefore ....
Answered by Reiny
that last line should say y = 3.5
Answered by Tia
I still do not understand it that well... I get what you did then I get confused at y=3/5.
Answered by Tia
Oh ok, that made a lot of sense. Thank you so much. Once you cleared it up.
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