My Math Forum  

Go Back   My Math Forum > High School Math Forum > Algebra

Algebra Pre-Algebra and Basic Algebra Math Forum


Thanks Tree3Thanks
  • 1 Post By greg1313
  • 1 Post By romsek
  • 1 Post By Denis
Reply
 
LinkBack Thread Tools Display Modes
May 3rd, 2017, 01:28 PM   #1
Member
 
Joined: Jan 2017
From: US

Posts: 86
Thanks: 5

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.
Indigo28 is offline  
 
May 3rd, 2017, 01:44 PM   #2
Global Moderator
 
greg1313's Avatar
 
Joined: Oct 2008
From: London, Ontario, Canada - The Forest City

Posts: 7,514
Thanks: 909

Math Focus: Elementary mathematics and beyond
Where are you having difficulty?
Thanks from romsek
greg1313 is offline  
May 3rd, 2017, 01:48 PM   #3
Senior Member
 
romsek's Avatar
 
Joined: Sep 2015
From: CA

Posts: 1,264
Thanks: 650

Quote:
Originally Posted by Indigo28 View Post
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.
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
Thanks from Indigo28
romsek is online now  
May 3rd, 2017, 01:51 PM   #4
Member
 
Joined: Jan 2017
From: US

Posts: 86
Thanks: 5

Thanks! I was having difficulty constructing the equation, but I think romsek answered my question.
Indigo28 is offline  
May 3rd, 2017, 02:22 PM   #5
Global Moderator
 
greg1313's Avatar
 
Joined: Oct 2008
From: London, Ontario, Canada - The Forest City

Posts: 7,514
Thanks: 909

Math Focus: Elementary mathematics and beyond
Quote:
Originally Posted by romsek View Post
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"?
greg1313 is offline  
May 3rd, 2017, 03:41 PM   #6
Senior Member
 
romsek's Avatar
 
Joined: Sep 2015
From: CA

Posts: 1,264
Thanks: 650

Quote:
Originally Posted by greg1313 View Post
I wanted Indigo28 to arrive at that, perhaps with some guidance.

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

I didn't see it until after I posted my answer.
romsek is online now  
May 3rd, 2017, 04:13 PM   #7
Global Moderator
 
greg1313's Avatar
 
Joined: Oct 2008
From: London, Ontario, Canada - The Forest City

Posts: 7,514
Thanks: 909

Math Focus: Elementary mathematics and beyond
You could have edited your post.
greg1313 is offline  
May 3rd, 2017, 06:12 PM   #8
Member
 
Joined: Jan 2017
From: US

Posts: 86
Thanks: 5

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.
Indigo28 is offline  
May 3rd, 2017, 06:49 PM   #9
Math Team
 
Joined: Oct 2011
From: Ottawa Ontario, Canada

Posts: 9,757
Thanks: 651

c = current speed

@(12+c)..............45..................>h hours
@(12-c)........27........>h hours

45 / (12+c) = 27 / (12-c)
Thanks from Indigo28
Denis is offline  
Reply

  My Math Forum > High School Math Forum > Algebra

Tags
algebra, current, inverse variation, solve, speed



Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
how to solve this speed problem davedave Algebra 3 February 23rd, 2017 11:01 PM
How to solve this speed problem? davedave Pre-Calculus 1 March 15th, 2015 10:18 PM
Find the ratio of his usual speed to his speed that day. Chikis Elementary Math 25 January 31st, 2014 09:48 AM
Find the speed of the current Chikis Elementary Math 2 May 22nd, 2013 08:06 PM
how to find current speed? peaceofmind Algebra 14 September 22nd, 2010 09:42 PM





Copyright © 2017 My Math Forum. All rights reserved.