If 5x-3y=23 and 4x-4y=20, which is the value of x+y?

3

Step-by-step explanation:

5x-3y=23

4x-4y=20

I'm going to try to set this up for elimination. I notice the bottom equation contains terms that are divisible by 4 so I'm going to divide both sides by 4 on that last equation only...

5x-3y=23

 x-  y=  5

Now I'm going to multiply the bottom equation by -3 so the y terms will be opposite. When you add opposites you do get 0.  That is the whole point of elimination.  

5x-3y=23

-3x+3y=-15

adding

2x+0=8

2x    =8

 x    =4

So  using that second equation x-y=5 I will find y given that x=4.

4-y=5

-y =1

 y=-1

So the solution to the system is (4,-1)

You are asked to find x+y

So x+y=4+(-1)=3

answer is:

1.75 pounds