Question

The sum of two numbers is 20. Their difference is 4. Write a system that describes this situation. Then solve your system by elimination to find the two numbers.

Answer 1

x+y = 20

x-y = 4

Solve: Add them two first -> 2x = 24 ->x = 12

So y = 8

Answer 2

Call the two numbers x and y. The equations are straightforward; you can convert directly from English into math. 

"The sum of the two numbers is 20": x + y = 20 

"Their difference is 4": x - y = 4 

Now you can solve. Adding the equations you get 2x = 24, so x = 12. That means y = 8