x-y=120 x+y=150

Question

addition to find the y value for this set of equations 

Answer 1

Hi Alex,

If we add these two equations, ys will be eliminated. then, we can find x. Then, we can plug it in one of the equations to solve for y. That is what I will do below.

 

x - y = 120

x + y = 150

+----------------

2x = 270

x = 135

 

x - y = 120

135 - y = 120

15 = y

y =15

Answer 2

Rewrite both equations so that x is isolated.

x = 120 + y

x = 150 - y

Since both [120 + y] and [150 - y] are equal to x, they must be equal to each other.

 

120 + y = 150 - y

2y = 30

 

y = 15

 

x = 135