wunder beta💰 Adding and Subtracting Decimals
Add and subtract decimals like 3.45 + 2.78, keep the decimal points lined up, and use number lines and models to see exactly what's happening.
2
lessons
~15 min
to learn
🔢 Math
subject
Ages 6–12
level
What you’ll learn
- Lining Up the PointsAdd and subtract decimals to hundredths by lining up the decimal points and regrouping.Line up the decimal points so each place value shares a column, then add right to left, carrying across the point when a column passes 9. 3.45 + 2.78 = 6.23. The classic trap is aligning by the end of the number instead of by place value - write 3.5 as 3.50 to stay safe.
- Models That Show the MathsModel decimal subtraction with a number line or base-ten blocks and connect it to the written method.Counting up on a number line, 2.67 hops to 3.00 (0.33) then to 5.03 (2.03), giving 2.36. Base-ten blocks and number lines make the place values visible, so the written method isn't a mystery. Different models all agree because place value never changes.
Questions this course answers
What is the golden rule for adding decimals in columns?
Aligning points keeps every place value in its column.
To add 3.5 + 2.78, how should you write 3.5?
Write 3.5 as 3.50 so the places line up.
For 5.03 - 2.67, a smart method is to...
Counting up turns the subtraction into friendly hops.
Why do models like number lines and blocks help with decimals?
Models reveal the meaning behind the digits.
Grounded in trusted sources
- Khan Academy
- BBC Bitesize - Maths
- NRICH - University of Cambridge
- Math is Fun
Every Wunder lesson is built from real, reputable sources — never invented.
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