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August 21, 2014

Homework Help: math,correction,help

Posted by jasmine20 on Saturday, January 13, 2007 at 3:19pm.

please can someone tell me where i am wrong.

Directions:
Translate to a system of equations and solve.
Problem:
Colored copies cost 10cents per copy and white copies cost 5cents per copy. Sandy made 400 copies, some of which were colored and the rest white. Her total bill wa $22.50. How many colored copies and how many white copies did she make?

My answer and solving this is what i get and the steps I used.

x for white coies and y for color
First equation:
x + y = 400
Second equation:
10x + 5y = 22.50

From the first equation i do the following to substitute for x:
x = 400 - y

so i substitute this into my second equation:
10(400-y)+5y = 22.50
4000-10y+5y=22.50
4000+5y=22.50
-4000 -4000
5y= -3977.50
--- --------
5 5

y = -795.50

so now i substituted this answer that i got for y into my first equation:

x + y = 400
x - 795.50 = 400
+ 795.50 +795.50
x = 1195.50


am i even doing this correctly or no.what am i doing wrong and which answer will be for my white and color copies because i don't see it.


I think you have mixed the units.
x+y=400 is ok.
For the second one, you have put in 10 cents and 5 cents but used dollars for the 22.50. You should change one or the other.
I would make it
0.10x + 0.05y=22.50
then solve for x and y.

so then, that means that there are 50 copies of white and 350 of color.

right

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