📖 The Lesson
Negative numbers are one of the trickiest topics on the GED — not because the math is hard, but because the problems are designed to look simpler than they are. This lesson covers two things: how to enter negative numbers correctly on your calculator, and how to avoid the most common mistake students make.
The main point: When you see a negative number in a problem, pause. Don't rush. Negative number problems are designed to catch students who move too fast. If you have access to a calculator — use it. Let the calculator do the arithmetic so you can focus on setting the problem up correctly.
Part 1 — Your Calculator
The negative sign and the subtraction sign are not the same button.
On the GED calculator, there are two different buttons you need to know:
The subtraction button is one of the four black operation buttons on the right side of the calculator. You use it when you're subtracting one number from another: 10 − 4.
The negative button ( - ) is a separate button that goes before a number to make it negative. You use it when the number itself is negative: (-) 3.
If you use the subtraction button when you mean a negative number, your calculator will give you the wrong answer — or an error. Always use the negative button to enter a negative number.
Part 2 — The Trap Most Students Fall Into
Most students know the multiplication and division sign rules cold:
negative × negative = positive negative × positive = negative
The problem is that a lot of students apply those same sign rules to addition and subtraction — and that's where things go wrong. The sign rules only apply to multiplication and division. Addition and subtraction work differently, and the results can surprise you.
Here are the four situations you'll run into. The key idea: think of subtraction as adding the opposite. And always check your work on the calculator.
Case 1
Positive − Positive
8 − 3
→ Adding the opposite: 8 + (−3) = 5
This one's familiar. No surprises here — you're just subtracting a smaller number from a bigger one. The answer is positive.
Case 2
Positive − Negative
8 − (-3)
→ Adding the opposite: 8 + 3 = 11
Subtracting a negative is the same as adding. The answer is bigger than what you started with — that surprises a lot of people.
Case 3
Negative − Positive
−8 − 3
→ Adding the opposite: −8 + (−3) = −11
Think of debt — you're starting $8 in debt and you borrowed $3 more. That makes you more in debt, not less. The answer goes further negative.
Case 4
Negative − Negative
−8 − (-3)
→ Adding the opposite: −8 + 3 = −5
This is the one that trips people up the most. Subtracting a negative means adding — you started at −8 and moved 3 steps in the positive direction.
The takeaway: When you see a subtraction problem with negatives, rewrite it as "adding the opposite" — then use your calculator to confirm. Don't trust sign-rule shortcuts for addition and subtraction. They don't apply.
🔢 Worked Examples
Example 1 — Subtracting a negative
Evaluate: −8 − (−3)
−8 − (−3)
= −8 + 3 (subtracting a negative = adding)
= −5
Example 2 — Mixed operations with negatives
Evaluate: (−4) × (−3) + (−2)
(−4) × (−3) + (−2)
= 12 + (−2) (negative × negative = positive)
= 12 − 2 (adding a negative = subtracting)
= 10
Reference
GED Formula Sheet
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📋 Open Formula Sheet
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