Complete the Vertical Calculation

Teaching Notes

Focus: Whole Number − Decimal. Use the worked example and teaching sequence below to explain the reasoning before independent practice.

Before You Begin

• Read the numbers and identify the operation.

Teaching Steps for Parents and Teachers

1. Align the decimal points and write equivalent trailing zeros when needed.
2. Subtract from the smallest place.
3. An exchange from one place gives ten units of the place immediately to its right, just as in whole-number subtraction.
4. Keep the decimal point aligned in the difference.
5. For a blank, identify the missing quantity. Substitute the completed value back into the original statement to check it.

Worked Examples

Evaluate 5-1.7.

1. Align the decimal points so corresponding places line up.
2. Use trailing zeros if needed, then calculate one place at a time.
3. 5 − 1.7 = 3.3

Answer: 3.3

Common Mistakes and How to Help

Adding a zero at the end of a decimal is allowed; moving its decimal point is not. Remember to reduce the place from which you exchanged one unit.

Add the difference to the amount subtracted. Compare the total with the original decimal.

Questions to Check Understanding

• Add the difference to the amount subtracted. Compare the total with the original decimal.
• Which step explains your answer?
• Can you apply the same reasoning when the numbers change?

Practice Advice

Work through the example together. Ask the learner to explain the first two problems, then try three independently. Review the first incorrect step before assigning more practice.

Next Practice

• Use New Numbers to practice the same skill with different values.
• If the learner needs help, return to the example and model each step before trying again.