Asked by help appreciated
The total time it takes for a canoe to go 3 miles upstream (against current) and back 3 miles downstream (with the current) is 4 hours. The current in the lake is 1 mile per hour. Find the speed of the canoe in still water.
Answers
Answered by
mathhelper
I think you have your times backwards.
Obviously it is going to take longer to go against
the current than it takes to go with the current.
I will assume you have typo and fix it.
speed of canoe in still water --- x mph
time to go upstream = 3/(x-1)
time to go downstream = 3/(x+1)
3/(x-1) + 3/(x+1) = 4
multiply by (x^2 - 1)
3(x+1) + 3(x-1) = 4x^2 -4
4x^2 - 6x - 4 = 0
2x^2 - 3x - 2 = 0
(x - 2)(2x + 1) = 0
x = 2 or x = -1/2, rejecting the negative answer,
x = 2
The boat can go 2 mph in still water
check:
time to go against current = 3/1 = 3 hours
time to go with the current = 3/3 = 1 hour, for a total of 4 hours
Obviously it is going to take longer to go against
the current than it takes to go with the current.
I will assume you have typo and fix it.
speed of canoe in still water --- x mph
time to go upstream = 3/(x-1)
time to go downstream = 3/(x+1)
3/(x-1) + 3/(x+1) = 4
multiply by (x^2 - 1)
3(x+1) + 3(x-1) = 4x^2 -4
4x^2 - 6x - 4 = 0
2x^2 - 3x - 2 = 0
(x - 2)(2x + 1) = 0
x = 2 or x = -1/2, rejecting the negative answer,
x = 2
The boat can go 2 mph in still water
check:
time to go against current = 3/1 = 3 hours
time to go with the current = 3/3 = 1 hour, for a total of 4 hours
Answered by
mathhelper
skip the first part of my answer:
"I think you have your times backwards.
Obviously it is going to take longer to go against
the current than it takes to go with the current.
I will assume you have typo and fix it."
I forgot to delete it from my post. I had typed that after
I misread your question initially.
"I think you have your times backwards.
Obviously it is going to take longer to go against
the current than it takes to go with the current.
I will assume you have typo and fix it."
I forgot to delete it from my post. I had typed that after
I misread your question initially.
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