What are the values of X, Y? 2X + 3Y = 9 X - Y = 4

Question

Solve the following simultaneous equations. What are the values of X, Y?
2X + 3Y = 9
X - Y = 4

Answer 1

 

Hi Kaylie:

This is a system of 2 simultaneous equations with 2 unknowns.

We can solve it by either substitution or elimination:

 

2X + 3Y = 9    {equation 1)
X - Y = 4         {equation 2}

 

To use elimination we can multiply equation 2 through

by 3 and add the equations to eliminate Y.

 

2x + 3y = 9

3x - 3y = 12

----------------

5x = 21

x = 21/5 or 4 1/5 or 4.2

 

Replace x with 21/5 in one of the original equations

and solve for y

2x + 3y = 9

2(21/5) + 3y = 9

3y = 9 - 42/5

3y = 45/5 - 42/5

3y = 3/5

y = (3/5)/3 = 3/15 = 1/5

 

x = 21/5 = 4 1/5

y = 1/5

 

Check:  x - y = 4

            4 1/5 - 1/5 = 4

           4 = 4