Question

Two numbers have a sum of 1212 and a difference of 518 what are are the two numbers

Answer 1

This question involves systems of equations. You can use matrices on a graphing calculator or solve by elimination. Set this up as x+y=1212 and x-y=518. If you solve on a graphing calculator, click 2nd matrix then edit. Change the matrix to a two by three and input on the first line horizontally 1, 1, 1212 and on the second line 1, -1, 518. Then hit the quit button and go to the home screen. Click 2nd matrix again and hit rref and quit again and click on the name of the matrix. If you solve by elimination multiply the first one by -1 so your ys can cancel and then find x and plug in. So your two numbers are 865 and 347. 

-Trust me, learn how to do these on your calculator, it will minus the tricky solving of systems.

Answer 2

So write down your 2 equations:
 x + y = 1212
 x - y = 518

If you add them together, the y's will cancel out, leaving you to solve for you x
2x = 1730
x = 865

then substitute x back into one of your equations to find y
ex: 865 + y = 1212, y = 347
ex: 865 - y = 518, -y = -347, y = 347