Add and Subtract Decimals with Aligned Places
Write the decimal quantities in aligned place-value columns.
About 25 minutes, plus any extended practice
Supplied materials
- Paper and a pencil; drawing and spoken explanations are welcome. An adult may read directions and options aloud.
- Supplied worked-case record: For 5.6−2.87, write 5.60−2.87.
- All quantities and shape descriptions are supplied in the worked example and questions; no purchase or personal information is needed.
Learn the idea
Decimal sums and differences combine equal units, so align decimal points and place values. Add trailing zeros when helpful without changing the amounts. Regrouping exchanges ten smaller units for one larger unit in addition or reverses that exchange in subtraction. Digit count alone does not tell where to align.
Write the decimal quantities in aligned place-value columns. Add or subtract the requested operation and show needed exchanges. Estimate using nearby whole values, then check exactly with the inverse operation.
Align decimal points, then add helpful trailing zeros. Aligning rightmost digits alone can mix unequal place units. Use tenths and hundredths columns to keep the unit sizes aligned.
- Use tenths and hundredths columns to keep the unit sizes aligned.
- Follow the worked example. Point to each number or shape feature and say what it tells you.
- Write the decimal quantities in aligned place-value columns.
- Try the question and then the three practice questions. Check your answers and explain any change you make.
See the method in action
For 5.6−2.87, write 5.60−2.87. Exchange to subtract hundredths and tenths, giving 2.73. Check 2.73+2.87=5.60. Aligning the final digits instead of decimal points would treat tenths as hundredths and change the intended values. Align decimal points, then add helpful trailing zeros. Aligning rightmost digits alone can mix unequal place units. Use tenths and hundredths columns to keep the unit sizes aligned.
Check your reasoning
Your answer is temporary and is not saved to an account. Download your current answer before leaving or reloading. Written work on paper or in another app stays in your own file.
Helpful tips
- Align decimal points, then add helpful trailing zeros.
- Aligning rightmost digits alone can mix unequal place units.
See the answer and explanation
6.15
Align matching decimal places, regroup if needed, and use an inverse check. The result is 6.15.
Take it further
Find 4.7+3.86 and 8.25−2.9. Expected: 8.56 and 5.35.
Nothing here is saved to an account or sent to a teacher. The answer download includes your current choice and any checked feedback. It does not include choices from the separate More practice section. Download that section separately.
More practice: try new cases
Choose an answer for each problem. Explain your method on paper, then use the feedback to decide what to revisit.
Your choices are temporary. Feedback appears after you check all the answers.
Nothing here is saved to an account or sent to a teacher. Keep your own notes or download them before leaving. The score describes these questions; it does not certify subject mastery.
Check the subject sources
These LifeStarter passages, scenarios and exercises are authored for this Academy with AI assistance and review. External resources keep their publishers’ terms. A grade label suggests a starting level; it does not establish alignment with your school’s complete requirements.