# Algebra - solve for x and y

• Nov 8th 2005, 03:44 PM
gilmoujr
Algebra - solve for x and y
I have two equations:

18x + 3y = 120
x + y = 15

I know that the answers are:

x = 5
y = 10

I could only solve it by punching in numbers and seeing if the problem was solved. I would like to know HOW to come about with the answer using Algebra.

Thanks...
• Nov 8th 2005, 04:03 PM
Jameson
Quote:

Originally Posted by gilmoujr
I have two equations:

18x + 3y = 120
x + y = 15

Are you familiar with substitution? In the second equation, can you solve for one variable to plug into the first equation?
• Nov 8th 2005, 04:18 PM
Jameson
Sigh. Ok, I'll get you started.

y=15-x. Now, make that substitution into your first equation and the answer should be apparent.
• Nov 8th 2005, 04:28 PM
gilmoujr
My humblest apologies. I actually remembered how to do it shortly after posting the question. When I came back (after explaining to my daughter how to do it), you had already responded. I appreciate the assistance that you provide (and this forum). I am going to bookmark it for my daughter's (and mine for that matter) reference. I searched the internet for over an hour before getting a hit to your site.

Again, thank you very much for the excellent forum.
• Nov 8th 2005, 04:32 PM
Jameson
Oh, sorry. I didn't mean to be disrespectful, it's just many people want a simple answer and don't care how it's done. I'm glad you are not one of those people :) .

Jameson :)