The sum of two numbers is 82 and their difference is 29. find each numbers.

System of Equations:
let these two numbers be x and y 

x+y = 82
x-y = 29

If you add the two equations you can eliminate y.

2x = 111
x= 55.5

Plug x back into one of the two equations. So the two numbers are 55.5 and 26.5.