SOLUTION: Brianna can paddle her kayak 5 miles per hour in still water. It takes her as long to paddle 9 miles upstream as it takes her to travel 21 miles downstream. Determine the speed of

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Question 407755: Brianna can paddle her kayak 5 miles per hour in still water. It takes her as long to paddle 9 miles upstream as it takes her to travel 21 miles downstream. Determine the speed of the river's current.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Brianna can paddle her kayak 5 miles per hour in still water.
It takes her as long to paddle 9 miles upstream as it takes her to travel 21 miles downstream.
Determine the speed of the river's current.
:
Let c = rate of the current
then
(5-c) = the speed upstream, (relative to the land)
and
(5+c) = the speed down stream
:
Write a time equation; time = dist/speed
:
upstr time = downstr time
9%2F%28%285-c%29%29 = 21%2F%28%285%2Bc%29%29
cross multiply
9(5+c) = 21(5-c)
45 + 9c = 105 - 21c
9c + 21c = 105 - 45
30c = 60
c = 60%2F30
c = 2 mph is rate of the current
:
:
Check this by finding the times, should be equal
9/3 = 3 hrs
21/7 = 3 hrs