# Substituting (URGENT!!)

##### New member
ok now I'm doing substituting:

x+y=5
5x-3y=17
________
-4x-2y=-12

thats what I got so far (the bottom equation) if anyone can tell me if it's right and maybe help me with the next step that would be great! Thanks

#### Gene

##### Senior Member
Well firstly the bottom equation is wrong. When you subtract -3y from y you get +4y.
1) x+y=5
2) 5x-3y=17
________
3) -4x+4y=-12
4) -x+y=-3

If you then add 1) & 4) you get
2y = 2
y=1
With no substitution.

For substitution you solve 1) for x
x=5-y
then substitute in 2) to get
5(5-y)-3y=17
Then you solve that for y and substitute in 1) and solve for x.

#### Denis

##### Senior Member
ok now I'm doing substituting:
x+y=5
5x-3y=17
________
-4x-2y=-12
thats what I got so far (the bottom equation) if anyone can tell me if it's right and maybe help me with the next step that would be great! Thanks
WHY did you subtract ? Is that the way you were taught? I HOPE NOT!

Multiply 1st equation by 3; now you have:
3x + 3y = 15
5x - 3y = 17
8x = 32 : OK?

IF you were TOLD to use substitution, then this way:
x+y=5 : y = 5 - x
Substitute that in 2nd equation:
5x-3y=17 : 5x - 3(5 - x) = 17 : 5x - 15 + 3x = 17 : 8x = 32 ; OK?

##### New member
Substituting (More) Still urgent!

It did thanks. I have another question:

7c+5d=18
c-5d=-2
________
6c=16
__ __
6 6

c=2 4/6= 2 2/3

Is that right so far?

#### jolly

##### Junior Member
Re: Substituting (More) Still urgent!

It did thanks. I have another question:

7c+5d=18
c-5d=-2
________
6c=16
__ __
6 6

c=2 4/6= 2 2/3

Is that right so far?
Why is everything always "urgent" with you? It gets old and annoying. FYI- New problems, new posts.

#### Gene

##### Senior Member
You seem to have problems with adding and subtracting. You are adding here. Why do you think that 7+1=6?????
And you still are not substituting. You are eliminating.