Rules for Adding and Subtracting Positive and Negative Values
- When we subtract a negative number we simply add the second number. Ex: 3- (-6) becomes 3 + 6 = 9
- When adding, if the signs are the same, we add the numbers and keep the sign. Ex: -7 + -8 = – 15
- When we subtract a positive, we can modify the problem so that we add a negative. -2 -5 becomes -2 + -5. Then we use rule number 2. Ex: -2 + -5 = -7
- When we are adding and the signs are different, we find the difference of the two numbers and keep the sign of the number with the greatest absolute value. Ex: -8 + 10. First we find the difference 10-8 =2. The answer is positive because 10 has a greater absolute value. The absolute value is the distance a number is away from zero on the number line.