Question

Solve
7x-3y=20
5x+3y=16
using substitution.

Answer 1

You don't need substitution for this.
Just add the equations together.

7x - 3y = 20
5x + 3y = 16
the y's cross out.
you get
12x = 36
x = 3
sub x into original equation to get the value of y.

Answer 2

if you had to use substitution you could
7x - 20 = 3y
7/3x - 20/3 = y
but it's fractions and using elimination you get whole numbers ( a whole lot neater, and less tedious)

Answer 3

I know, but I used elimination on it before, now I wanted to use substitution.

Answer 4

Okay.
then sub for y with the given
7/3 x - 20/3 = y
5x + 3(7/3x - 20/3) = 16
just a hint since everything is multiplied by 3 and there are three in the denominators they cancel leaving just the top left.
so
5x + 7x - 20 = 16

Answer 5

x = 3

Answer 6

yep.

Answer 7

How do i solve for y now? Walk me through this.

Answer 8

Nevermind. I'll just do the adding. How do i solve for y using addition?

Answer 9

addition?

Answer 10

you mean elimination?

Answer 11

you're making things complicated if you wanted to solve for y first.
7x-3y=20
5x+3y=16
it would be best to solve for x and sub the value of x in and then find y.

Answer 12

Lol. Okay, fine. How do I solve this with substitution.

Answer 13

Shammmy.

Answer 14

solve what?

Answer 15

I want to get Y.

Answer 16

you already your x value which is 3.
so
7(3) - 3y = 20
evaluate and solve for y

Answer 17

\[y = \frac{ 1 }{ 3 }\]

Answer 18

yep