ADDITION OF INTEGERS:
1) If the addends have the same signs, add, then copy the common sign for the sum. Example (-4) + (-5) = -9 (negative is the common sign)
2.) If the addends have different signs, subtract (just like when you subtract smaller number from the bigger number) then copy the sign of the number which larger (when not considering its sign).
Example: (-10) + (4) = -6
SUBTRACTION OF INTEGERS (It's also addition).
1.) Change the sign of the subtrahend, then proceed to addition rule.
Example: (-130) - (30) = N
Change the sign of 30, the subtrahend, then add the integers.
(-130) + (-30) = 1 160
150 - 60 = N
150 + (-60) = 90