SOLUTION: It took Jeremy and Kirk five hours to canoe 32 miles downstream on the upper Blue River. The next day it took them seven hours to canoe upstream for 21 miles. What was the speed o

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Question 578639: It took Jeremy and Kirk five hours to canoe 32 miles downstream on the upper Blue River. The next day it took them seven hours to canoe upstream for 21 miles. What was the speed of the current, and what was their average speed in still water?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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It took Jeremy and Kirk five hours to canoe 32 miles downstream on the upper Blue River.
The next day it took them seven hours to canoe upstream for 21 miles.
What was the speed of the current,
:
Let c = the speed of the current
Let s = canoes speed in still water
then
(s-c) = effective speed upstream
and
(s+c) = effective speed downstream
:
Write a distance equation for each trip: dist = time * effective speed
5(s+c) = 32
and
7(s-c) = 21
simplify divide both sides by 7
s - c = 3
s = (c+3)
replace s with (c+3) in the 1st equation
5((c+3) + c) = 32
5(2c+3) = 32
10c + 15 = 32
10c = 32 - 15
10c = 17
c = 1.7 mph is the speed of the current
:
"and what was their average speed in still water?"
s - 1.7 = 3
s = 3 + 1.7
s = 4.7 mph is the speed in still water
:
:
Check this in 2nd original equation
7(s-c) = 21
7(4.7-1.7) = 21