To subtract means to take away a number from another number to find the difference between them. We model subtracting a positive integer on the number line by moving left. We also model the addition of a negative integer on the number line by moving left. When we compare the number line models for the equations 15 – 5 = 10 and 15 + (-5) = 10, we see that they look the same. 5 and -5 are additive inverses. This shows that subtracting an integer is the same as adding its additive inverse.