Date: Fri, 18 Nov 1994 07:58:28 -0800 From: (Paul Pragin) Subject: dr.math Hi. My name is Paul. How do you do this? 2y+10x=180 4x+4y=100 Please explain how you do this system.
Date: Fri, 18 Nov 1994 11:48:19 +0000 From: Elizabeth Anna Weber Subject: Re: dr.math Hi Paul! Thanks for writing to Dr. Math. To solve a system of equations, first solve for one variable. 4x+4y=100, so 4x=100-4y, and we have x=25-y Now that we know something about x, let's see if we can use this to find out some more about y. 2y+10x=180, and we can substitute something for x, now 2y+10(25-y)=180, so 2y+250-10y=180. Combining a few terms, we have -8y=-70, so y=70/8 Remember, we said x=25-y So, x=25-(70/8) x=200/8-70/8 x=130/8 If we go back to our original equations, we can check that this works: 4x+4y=100 4(130/8)+4(70/8)=100 130/2+70/2=100 200/2=100 100=100 Now, can you solve these systems? 4y+6x=80 8x+3y=120 3y+4x=60 9x+2y=150 --Elizabeth Weber, doctor on call
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.