Posted by **peyton** on Saturday, September 24, 2011 at 5:19pm.

x+2y=3

5x+4y=8

I isolated x+2y=3 to make: x=3-2y

then i began to sub in equation one with equation two:

5x+4y(3-2y)=8

5x+12-8y=8

after that i began to try to solve the equation but my answers were not correct. any help would be greatly appreciated!

- Grade 10-Math -
**Reiny**, Saturday, September 24, 2011 at 6:20pm
You are substituting for y instead of x

Besides that you were still keeping the y as well.

5(3-2y) + 4y = 8

15 - 10y + 4y = 8

-6y = -7

y = 7/6

then in x = 3-2y

x = 3-14/6 = 2/3

x = 2/3 , y = 7/6

- Grade 10-Math -
**peyton**, Sunday, September 25, 2011 at 3:55pm
i understand how you got the answer i just don't get why i don't put 5x+4y before the equation because i have been for all the other ones and i got those ones right..

for example this one:

6x+5y= 7

x-y= 3

i isolated the second equation into y=3+x

so: 6x+5y(3+x)=7

6x+15+5x=7

6x+5x-15+15=7+15

11/11= 22/11

x=2

then i subbed in the other equation..

6(2)+5y=7

12+5=7-12

5y/5= -5/5

y= -1

and i checked my answer and it was correct.

i just don't understand what i'm doing wrong for the equation.. because i keep thinking the full equation must go first not separate it.

- Grade 10-Math -
**Penny**, Monday, September 26, 2011 at 1:59pm
Horizontal line through(5,0)

- Grade 10-Math -
**Anonymous**, Tuesday, April 30, 2013 at 4:58pm
-2(2y+15)<-6y-14

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