My Math Forum Inverse Proportion Problem
 User Name Remember Me? Password

 Algebra Pre-Algebra and Basic Algebra Math Forum

 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: 12,131 Thanks: 431 Math Focus: Calculus/ODEs Re: Inverse Proportion Problem We are told: y is inversely proportional to 4x + 5 hence, we may state: (1) $y(4x+5)=k$ We are given: y = 4 when x = 8 1/2 = 17/2 Substituting these values for x and y into (1), we obtain: $4$$4\(\frac{17}{2}$$+5\)=k$ $4$$2\cdot17+5$$=k$ $4(40-1)=k$ $k=160-4$ $k=156$ When $y=12$ we have by substitution into (1) and using the value we found for k: $12(4x+5)=156$ Solve for x. First divide both sides by 12: $4x+5=13$ Subtract through by 5: $4x=8$ Divide through by 4: $x=2$
 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 40-1 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: 12,131 Thanks: 431 Math Focus: Calculus/ODEs Re: Inverse Proportion Problem $2\cdot17+5=34+5=39=40-1$ I used 40 - 1 to make the multiplication easier. I am using $\LaTeX$ to write the mathematical expressions.

 Tags inverse, problem, proportion

,

how to solve word problemwith continued proportions

Click on a term to search for related topics.
 Thread Tools Display Modes Linear Mode

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

 Contact - Home - Top