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March 29th, 2014, 07:00 AM  #1 
Newbie Joined: Mar 2014 From: London Posts: 2 Thanks: 0  Really need your help with these questions guys!!!!
1. Z is proportional to X. When X = 4, Z = 2. Enter the value of X required to give Z = 2. 2. Y is proportional to X. When X = 2, Y = 1. Find the value of X required to give Y = 4. 3. Z is proportional to (X  2). When X = 1, Z = 1. Enter the value of X required to give Z = 2. 4. Y is proportional to (1  X). When X = 2, Y = 2. Find the value of X required to give Y = 6. 5. Y is inversely proportional to X. When X = 2, Y = 1. Find the value of X required to give Y = 6. [Express your as a decimal correct to 2sf] 6.C is inversely proportional to A^2. When A = 0.1, C = 50. Find C when A = .02. This might help =IMPORTANT NOTE In the following, x^2, x^3, mean "x squared", "x cubed", respectively. Generally, a^n means "a to the power n". 
March 29th, 2014, 07:12 AM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 520 Math Focus: Calculus/ODEs 
I'll show you how to do the first, and then see if you can do the rest in like manner. 1. Z is proportional to X. When X = 4, Z = 2. Enter the value of X required to give Z = 2. The first statement means we may write: Using the given data, we may then write: Solving for k, we find: And so the relationship between Z and X is: Now, we let Z = 2 and solve for X: 
March 29th, 2014, 07:13 AM  #3  
Newbie Joined: Mar 2014 Posts: 13 Thanks: 6  Quote:
I will give you the equations for each proportion and see if you can go from there: Direct Proportion: y = kx Inverse proportion: y = k/x With Squares: y = kx^2 OR in your case since it's inversely proportional: C = K/A^2 Just as a hint, you have to find K first before making the proportion. To make things simple, the following link describes in great detail how to go about these kinds of problems. If you need more specific help, let us know. Directly Proportional and Inversely Proportional Last edited by Harbinger; March 29th, 2014 at 07:19 AM.  

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