Computing -8 - (-3)

Pre-Algebra · Axiom Academy

EXAMPLE Computing an Integer Subtraction Subtracting a negative, step by step — with a number line and a charge model to see why. Compute the integer subtraction -8 - (-3) . We will rewrite it using the "add the opposite" rule, then confirm the result two ways: on a number line and with a charge model. Start at -8 (red), move right 3 units (adding +3 ) and land on -5 (green). Each of the 3 positives cancels one negative (faded). 8 - 3 = 5 negatives remain, so the result is -5 . Nice work. You computed -8 - (-3) and checked it two ways. Remember: The rule: subtracting a negative is the same as adding the positive — `a - (-b) = a + b`. Number line: adding a positive number means moving to the right. Charge model: one positive and one negative cancel each other out. The result: `-8 - (-3) = -8 + 3 = -5`. This "add the opposite" move shows up everywhere once you start solving equations and working with integers.

This is the written version of the interactive lesson above. See the full Pre-Algebra course.