January 25, 2015

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.

Translate to a system of equations and solve.
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 -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.


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