Adding and Subtracting Decimals
Add and subtract decimal numbers by lining up decimal points
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Adding and Subtracting Decimals
The Golden Rule
Always line up the decimal points!
This is the most important thing to remember when adding or subtracting decimals.
Adding Decimals
Example:
| Step | What to do |
|---|---|
| 1. Line up decimals | Stack the numbers with decimal points aligned |
| 2. Add placeholder zeros | Write as |
| 3. Add column by column | Start from the right |
| Answer |
Tip: Add zeros as placeholders so both numbers have the same number of decimal places!
Subtracting Decimals
Example:
| Step | What to do |
|---|---|
| 1. Line up decimals | Stack the numbers with decimal points aligned |
| 2. Add placeholder zeros | Write as |
| 3. Subtract column by column | Borrow when needed |
| Answer |
Money Problems
Decimals are used with money all the time!
Example: You have \20.00$12.75$. How much is left?
You have \7.25$ left.
Example: You buy items for \3.49$5.25$1.99$. What's the total?
Total: \10.73$
Word Problem Strategy
- Read carefully — decide whether to add or subtract
- Line up the decimal points — always!
- Add placeholder zeros if the numbers have different decimal places
- Check your answer — does it make sense?
- Label your answer — include units (dollars, meters, etc.)
Practice Tips
- Estimation helps: Round to whole numbers first to check if your answer is reasonable
- Common mistake: Forgetting to line up the decimals — this leads to wrong answers every time!
- Money is great practice: Use receipts and price tags to practice adding decimals
📚 Practice Problems
1Problem 1easy
❓ Question:
Calculate:
💡 Show Solution
Solution:
Line up the decimal points:
&5.6 \\ + &2.8 \\ \hline &8.4 \end{align}$$ **Answer:** $8.4$2Problem 2easy
❓ Question:
Calculate:
💡 Show Solution
Solution:
Line up the decimal points:
&5.6 \\ + &2.8 \\ \hline &8.4 \end{align}$$ **Answer:** $8.4$3Problem 3medium
❓ Question:
Sarah ran 3.75 miles on Monday and 5.4 miles on Tuesday. How many total miles did she run?
💡 Show Solution
Solution:
Add the distances:
&3.75 \\ + &5.40 \\ \hline &9.15 \end{align}$$ **Answer:** 9.15 miles4Problem 4medium
❓ Question:
Sarah ran 3.75 miles on Monday and 5.4 miles on Tuesday. How many total miles did she run?
💡 Show Solution
Solution:
Add the distances:
&3.75 \\ + &5.40 \\ \hline &9.15 \end{align}$$ **Answer:** 9.15 miles5Problem 5hard
❓ Question:
Tom had \50.00$12.95$18.50$. How much money does he have left?
💡 Show Solution
Solution:
Step 1: Find total spent
&12.95 \\ + &18.50 \\ \hline &31.45 \end{align}$$ Step 2: Subtract from original amount $$\begin{align} &50.00 \\ - &31.45 \\ \hline &18.55 \end{align}$$ **Answer:** $\$18.55$6Problem 6hard
❓ Question:
Tom had \50.00$12.95$18.50$. How much money does he have left?
💡 Show Solution
Solution:
Step 1: Find total spent
&12.95 \\ + &18.50 \\ \hline &31.45 \end{align}$$ Step 2: Subtract from original amount $$\begin{align} &50.00 \\ - &31.45 \\ \hline &18.55 \end{align}$$ **Answer:** $\$18.55$Practice with Flashcards
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