My Math Forum Solve For the Speed Of The Current

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 May 3rd, 2017, 01:28 PM #1 Senior Member   Joined: Jan 2017 From: US Posts: 111 Thanks: 6 Solve For the Speed Of The Current A fish can swim 45 miles downriver in the same amount of time that it can swim 27 miles upriver. Solve for the speed of the current if the speed of the fish is 12 mph in still water. Show all of your work and explain your solution.
 May 3rd, 2017, 01:44 PM #2 Global Moderator     Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,814 Thanks: 1046 Math Focus: Elementary mathematics and beyond Where are you having difficulty? Thanks from romsek
May 3rd, 2017, 01:48 PM   #3
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Quote:
 Originally Posted by Indigo28 A fish can swim 45 miles downriver in the same amount of time that it can swim 27 miles upriver. Solve for the speed of the current if the speed of the fish is 12 mph in still water. Show all of your work and explain your solution.

clearly the current is in the direction of down river

$v_{up} = v_{still}-v_{current}$

$v_{down} = v_{still}+v_{current}$

$v = \dfrac d t$

$t=\dfrac d v$

$\dfrac{45}{ v_{still}+v_{current}}=\dfrac{27}{ v_{still}-v_{current}}$

see if you can finish

 May 3rd, 2017, 01:51 PM #4 Senior Member   Joined: Jan 2017 From: US Posts: 111 Thanks: 6 Thanks! I was having difficulty constructing the equation, but I think romsek answered my question.
May 3rd, 2017, 02:22 PM   #5
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Quote:
 Originally Posted by romsek velocities add clearly the current is in the direction of down river $v_{up} = v_{still}-v_{current}$ $v_{down} = v_{still}+v_{current}$ $v = \dfrac d t$ $t=\dfrac d v$ $\dfrac{45}{ v_{still}+v_{current}}=\dfrac{27}{ v_{still}-v_{current}}$ see if you can finish
I wanted Indigo28 to arrive at that, perhaps with some guidance.

Why did you ignore my post, other than clicking "Thanks"?

May 3rd, 2017, 03:41 PM   #6
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 Originally Posted by greg1313 I wanted Indigo28 to arrive at that, perhaps with some guidance. Why did you ignore my post, other than clicking "Thanks"?

I didn't see it until after I posted my answer.

 May 3rd, 2017, 04:13 PM #7 Global Moderator     Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,814 Thanks: 1046 Math Focus: Elementary mathematics and beyond You could have edited your post.
 May 3rd, 2017, 06:12 PM #8 Senior Member   Joined: Jan 2017 From: US Posts: 111 Thanks: 6 I'm just saying... I posted this question hoping for helpful steps to get to the solution. I don't see why there is a problem with what Romsek posted, and it's not because I'm trying to cheat. He didn't even give the answer, if demonstrated how to set up the formulas. If you're a moderator and feel there is sincerely a problem with what he posted, fine. But I don't see what the problem is. Last edited by Indigo28; May 3rd, 2017 at 06:24 PM.
 May 3rd, 2017, 06:49 PM #9 Math Team   Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 12,621 Thanks: 845 c = current speed @(12+c)..............45..................>h hours @(12-c)........27........>h hours 45 / (12+c) = 27 / (12-c) Thanks from Indigo28

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