simultaneous equations

Question

X=Y-15 , X+Y-15=145 how do i get X and Y

Answer 1

Rewrite the equations:

X-Y=-15

X+Y=160 because 145+15=160.

Now, add the two equations:

2X=160-15=145, X=145/2.

X+Y=160 becomes Y=160-X=160-145/2=(320-145)/2=175/2.

So the solution is X=145/2 and Y=175/2.

Or, X-Y=-15 becomes Y=X+15=145/2+15=(145+30)/2=175/2.