Money and Decimal Operations

Overview

In this 45-minute lesson, the student adds and subtracts money in real-world situations involving prices, totals, and change. The lesson builds on place-value understanding by connecting whole-dollar amounts to decimals written to the hundredths and using addition-subtraction relationships to check answers.

Learning intentions

Students will be able to:

• Add and subtract money by aligning decimal points.
• Represent whole-dollar amounts with two decimal places.
• Solve one- and two-step problems involving prices, totals, and change.
• Explain how place value and inverse operations support accurate calculations.

Success criteria

• I can write $7 as $7.00 and align decimal points correctly.
• I can add or subtract money to the hundredths.
• I can label my answer with a dollar sign and explain what it means.
• I can check subtraction with addition or estimate to decide whether my answer is reasonable.

Curriculum links

• Number and Operations in Base Ten — add and subtract decimals to hundredths using place value, models, and written methods.
• Number and Operations in Base Ten — explain the relationship between adjacent place values and the effect of multiplying or dividing by powers of 10.
• Number and Operations in Base Ten — read and write decimals through expanded and place-value representations.
• Number and Operations in Base Ten — use the relationship between addition and subtraction to check calculations.

Lesson structure (45 minutes)

1. 0–5 min · Hook and retrieval. Display the opening money comparison slide showing a receipt with prices such as $4.50, $7, and $2.08, alongside the question, “Which amount is greatest, and how do you know?” Ask the student to write $7 using two decimal places and explain the value of each digit. The student compares the amounts, writes $7.00, and explains that the zero records no hundredths.

2. 5–13 min · Model place value and alignment. Use the place-value and worked-example slides to model $7.00 + $4.58 and $12.00 − $3.75. Emphasize that decimal points are aligned because ones must be added to ones and hundredths to hundredths; connect this to the fact that each place is ten times the value of the place to its right. The student represents each equation in a place-value chart, predicts an estimate, and then follows the written method.

3. 13–18 min · Guided reasoning. Reveal the guided practice prompt: “A notebook costs $3.79 and a pen costs $1.25. What is the total?” Ask, “Why should the decimal points be directly underneath each other?” Then pose, “If you pay with $10.00, how can subtraction help you find the change?” The student solves aloud, labels the total and change, and checks the subtraction by adding the change to the purchase total.

4. 18–33 min · Independent application. Distribute the money and decimal operations practice sheet. The student completes problems involving adding two or three prices, subtracting a purchase from a whole-dollar amount, finding change, and explaining one solution with an equation or place-value drawing. Prompt the student to estimate first, write whole-dollar amounts with two decimal places, and use addition to check at least one subtraction. Confer briefly after the first two questions and address any misconception before the student continues.

5. 33–39 min · Error analysis and discussion. Show the error-analysis and discussion slides with the incorrect calculation $8.50 − $2.75 = $6.25 Ask the student to decide whether the answer is correct, identify the error or confirm the reasoning, and prove the conclusion using addition or an estimate. The student corrects the work if needed and explains the checking strategy in complete sentences.

6. 39–45 min · Exit check and closure. Use the final reflection and exit-question slide. The student completes the worksheet exit questions: write $9 as a decimal to the hundredths, solve $15.00 − $6.48, and explain how addition can check the answer. Finish by asking the student to state one rule for working with money and one way to tell whether an answer is reasonable.

Resources

• the complete money and decimal operations slide deck
• the money and decimal operations practice sheet
• Place-value chart
• Base-ten or decimal grid model
• Pencil and scratch paper
• Optional classroom calculator for checking after work is shown
• Teacher observation checklist

Assessment

• During modeling and guided practice, check whether the student writes whole-dollar amounts with two decimal places and aligns decimal points rather than digit edges.
• Review the worksheet for accurate computation, appropriate dollar notation, estimates, and a subtraction check using addition.
• Use the final three-question exit check to determine whether the student can transfer the method independently. If errors occur, have the student locate the place-value or regrouping step before correcting the answer.

Differentiation

• For support, provide a labeled place-value chart, allow the student to use a decimal grid, and use the sentence starters: “I aligned the decimal points because…” and “I checked my subtraction by…”
• Reduce the number of worksheet problems while requiring the student to explain each completed problem. Model regrouping with money notation before returning to the written algorithm.
• For an individual student, use immediate feedback and think-aloud questioning rather than group discussion; ask the student to verbalize each place-value decision.
• For extension, ask the student to create a receipt with three items, a whole-dollar payment, and a change amount, then prove the change using addition and estimation.