Addition of signed numbers
You already know that the sum of two positive integers is a positive integer.
The rules below will help you find the sign of the sum of two negative integers and the sign of the sum of a positive and a negative integer.
Adding Integers with the Same Sign 
To add integers with the same sign, add their absolute values. Give the result the same sign as the integers. 
Adding Integers with Different Signs 
To add integers with different signs, subtract their absolute values. Give the result the same sign as the integer with the greater absolute value. 
Calculate:
a. 16 + (4)
Add the absolute values.
Give the result the same sign as the integers.
16 + (4) = 20

b. 30 + 5
Subtract the absolute values.
The result is negative because
30>5.
30 + 5 = 25

Addition of several integers
(+2) + (3) + (4) = 2 3 4 =2 7 = 5
(12) + (4) + (+8) = 12  4 +8 = 16 +8= 8