Question

Y=2x-3
x+y=18
solve for x
solve for y
X= ?
Y=?

Answer 1

2X-Y=3
X+Y=18

2x-y=3
X+y=18

Substitution method
X=18 -y
Substitutes Y in the question 1 to get X
2(18-y)-y=3
36-2y-y=3
36-3y=3
Collect like terms
36-3=3y

33=3y
Divide both side by 3

Y=11

Substitute y in the equation 1to get X
2X-11=3
Clt
2X= 3+11
2x=14

Divide both sides by 2

X=7

Therefore, x=7 and y=11

Answer 2

x=7, y=11

Explanation:

Using simultaneous equations we can sub y in equation 1 into equation 2.

Equation 1. y=2x-3

Equation 2. x+y=18

Since y=2x-3 we can replace it so that

2'. x+2x-3=18

Now simplify

= 3x-3=18

Add 3 onto both sides to undo the subtraction of 3 so that,

3x=21

Now divide both sides by three to undo the multiplication of 3 so that,

x=7

Now sub in x (which is 7) into one of the equations to find y

7+y=18

To undo the five, subtract 7 from both sides so that

y=11