
Algebra PreAlgebra and Basic Algebra Math Forum 
 LinkBack  Thread Tools  Display Modes 
August 11th, 2012, 01:09 AM  #1 
Joined: Jul 2010 Posts: 69 Thanks: 0  Inverse Proportion Problem
Hello, I have a problem that I would not have been able to figure out if it were not for tutors. The problem is that after trying so hard to figure this math problem out on my own, I cannot see how it is done. Here we have the word problem of: If y is inversely proportional to 4x + 5 and y = 4 when x = 8 1/2, find x when y = 12. If someone could help me solve this problem I would appreciate it. I also will ask, if you get the problem correct, how you did it. Thanks. 
August 11th, 2012, 01:41 AM  #2 
Global Moderator Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 11,808 Thanks: 267 Math Focus: The calculus  Re: Inverse Proportion Problem
We are told: y is inversely proportional to 4x + 5 hence, we may state: (1) We are given: y = 4 when x = 8 1/2 = 17/2 Substituting these values for x and y into (1), we obtain: When we have by substitution into (1) and using the value we found for k: Solve for x. First divide both sides by 12: Subtract through by 5: Divide through by 4: 
August 11th, 2012, 11:39 AM  #3 
Joined: Jul 2010 Posts: 69 Thanks: 0  Re: Inverse Proportion Problem
MarkFL, You got the answer correct. Where did the 401 come from? Also, how are you using those fraction symbols? 
August 11th, 2012, 01:18 PM  #4 
Global Moderator Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 11,808 Thanks: 267 Math Focus: The calculus  Re: Inverse Proportion Problem I used 40  1 to make the multiplication easier. I am using to write the mathematical expressions. 

Tags 
inverse, problem, proportion 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
continued proportion  empiricus  Algebra  8  September 20th, 2011 11:40 AM 
Direct proportion  MathematicallyObtuse  Algebra  4  January 15th, 2011 08:26 PM 
Proportion  haftakhan  Algebra  2  July 5th, 2010 01:49 PM 
What proportion  Mahonroy  Advanced Statistics  2  September 8th, 2009 08:39 AM 
inverse proportion  logical  Elementary Math  1  June 24th, 2009 10:49 PM 