Adding, Subtracting & Multiplying Decimals
Week 2 · Decimal Operations
Master decimal operations by keeping digits lined up and tracking the decimal point.
Adding and Subtracting Decimals\n\nThe most important rule: **line up the decimal points!**\n\nThen add or subtract as you would whole numbers.\n\n**2.75 + 3.4**\n```\n 2.75\n+ 3.40\n------\n 6.15\n```\nAdd a zero placeholder so both numbers have the same number of decimal places.\n\n## Multiplying Decimals\n\n1. Ignore the decimal points and multiply as whole numbers\n2. Count the total decimal places in both factors\n3. Place the decimal point that many places from the right in your answer\n\n**1.2 × 3.4**\n- 12 × 34 = 408\n- Total decimal places: 1 + 1 = 2\n- Answer: 4.08
Worked Examples
Example 1
📝 2.75 + 3.4
✓ Answer: 6.15
Line up decimals: 2.75 + 3.40 = 6.15
Example 2
📝 1.2 × 3.4
✓ Answer: 4.08
12 × 34 = 408. Two total decimal places → 4.08
Common Mistakes to Avoid
- ⚠️Forgetting to line up decimal points when adding/subtracting
- ⚠️Miscounting decimal places when multiplying
- ⚠️Not adding zero placeholders (3.4 vs 3.40)