Mission 8 · Unit 4

Decimal Operations

6.NS.B.3 · Unit 4
Today's objective: Add, subtract, multiply, and divide multi-digit decimals.
Need a hint?
Re-read the problem and underline the numbers and the question. Pick one representation (model, table, or equation), show your steps, and check that your answer makes sense for the situation.

The school cafeteria is planning a new healthy lunch menu. Your team has been hired as the menu consultants. Each meal must cost exactly $4.75 or less per student. The cafeteria manager gave you ingredient prices: turkey slices at $0.85 each, whole wheat rolls at $0.42 each, carrot packs at $0.68 each, apple juice boxes at $1.15 each, and yogurt cups at $0.93 each. Your team must design a lunch combo, calculate the exact total cost, and figure out how many full lunches can be made with a $142.50 budget.

Turkey $0.85 Roll $0.42 Carrots $0.68 Juice $1.15 Yogurt $0.93 Budget: $142.50 Meal Limit: $4.75 each

Investigation

The Problem: Design a lunch combo using at least 3 of the 5 ingredients. The combo must cost $4.75 or less per meal. Then calculate: how many complete lunches can be served with a $142.50 budget? How much money is left over?

Visual Model: Decimal Place Value Chart

Ones . Tenths Hundredths Turkey 0 . 8 5 $0.85 Roll 0 . 4 2 $0.42 Carrots 0 . 6 8 $0.68 Juice 1 . 1 5 $1.15 Yogurt 0 . 9 3 $0.93 ALL 5 4 . 0 3 $4.03

Step-by-Step Investigation Guide

  1. List the ingredients and prices. Write each price lined up by the decimal point. Make sure every price has two decimal places. Why does lining up the decimal points matter when you add?
  2. Choose your combo. Pick at least 3 items. Add the prices using the place value chart. Start with the hundredths column, then tenths, then ones. Regroup (carry) if any column is 10 or more. Does your combo total stay at or below $4.75?
  3. Check with subtraction. Subtract your combo total from $4.75. If the answer is 0 or positive, your combo works. If negative, remove or swap an item. What is $4.75 minus your total? What does that leftover money mean?
  4. Divide the budget. Divide $142.50 by your combo cost. This tells you how many full lunches you can make. Write the quotient and remainder. What does the remainder represent in this situation? Can you serve a "partial" lunch?
  5. Calculate leftover money. Multiply the number of full lunches by the combo cost. Subtract that product from $142.50 to find leftover money. How can you check your division is correct using multiplication?
  6. Compare combos. Does a different 3-item combo serve more students? Try at least one other combo and compare the number of lunches. Is it better to serve more students a cheaper meal or fewer students a more complete meal?

Language Support: Key Vocabulary

decimal — a number with a dot (.) that shows parts smaller than one (example: 3.25)
place value — the value of a digit based on its position (ones, tenths, hundredths)
sum — the answer when you add numbers together
difference — the answer when you subtract one number from another
product — the answer when you multiply numbers together
quotient — the answer when you divide; how many equal groups you can make
remainder — the amount left over after dividing into equal groups
budget — the total amount of money you are allowed to spend

Sentence Frames

"The sum of _____ and _____ is _____ because I added the hundredths first, then the tenths, then the ones."

"When I divide $142.50 by _____, the quotient is _____ with a remainder of _____. This means we can make _____ full lunches."

"Our combo costs _____ per meal, which is _____ (under/over) the $4.75 limit by _____."

Multiple Representations

Place Value Chart

Line up each price in a column chart with ones, tenths, and hundredths. Add column by column from right to left. This shows regrouping clearly.

Best for: seeing how digits combine in each place

Equation Chain

Write the operations as equations:
$0.85 + $0.42 + $1.15 = $2.42
$142.50 / $2.42 = ?
Chain each step so the answer from one becomes the input for the next.

Best for: showing the logical order of calculations

Comparison Table

Make a table with columns: Combo Items, Total Cost, Under Budget?, Number of Lunches, Leftover Money. Fill in rows for 2-3 different combos and compare.

Best for: deciding which combo is the best choice

Team Roles

Facilitator Keeps the group on track, watches the phase timer, makes sure everyone speaks. Mission 8 task: Make sure the team picks a combo, checks the budget limit, AND answers how many lunches can be made.
Model Builder Creates the place value chart, writes the equations, and draws the comparison table. Mission 8 task: Build a clear place value addition chart showing regrouping for the combo total.
Precision Checker Checks every calculation, makes sure decimal points are lined up, and verifies the answer is reasonable. Mission 8 task: Use estimation to check: is $0.85 + $0.42 + $1.15 close to $1 + $0.50 + $1 = $2.50? Does the division check out with multiplication?
Reporter Prepares the defense with claim, evidence, and one mistake the team caught and fixed. Mission 8 task: Explain which combo the team chose, why it is the best use of the budget, and how many students it feeds.

Timed Lab Phases

Ready
Click a phase, then press Start.
03:00

Read the scenario out loud. Assign roles. Underline the key numbers: $4.75 limit, five ingredient prices, and $142.50 budget.

  • Circle all the decimal numbers in the problem.
  • Decide which operation you will use first (addition).
  • Which items look the most expensive? Least expensive?
Checkpoint: Every teammate can name the budget limit and at least 3 prices.

Build your model. Choose your combo items. Set up a place value chart and add the prices. Line up decimal points carefully.

  • Write each price in the chart: ones | tenths | hundredths.
  • Add the hundredths column first. Do you need to regroup?
  • Check: is your total at or below $4.75?
  • If over budget, swap one item and recalculate.
Checkpoint: The team has a combo total that is $4.75 or less, shown in a place value chart.

Divide the budget by your combo cost. Find how many full lunches the cafeteria can serve. Calculate the leftover money.

  • Set up: $142.50 divided by your combo price.
  • Write the quotient (whole lunches) and remainder (leftover money).
  • Check: quotient times combo price + remainder = $142.50?
  • Try a second combo. Which one feeds more students?
Checkpoint: The team has a clear answer: number of lunches and leftover dollars.

Prepare your presentation. Write a claim, show your evidence, and explain one mistake you caught.

  • State your combo, its cost, and how many lunches it makes.
  • Point to the place value chart as your evidence.
  • Explain: why is this the best combo for the budget?
  • Share one error the Precision Checker found and how you fixed it.
Checkpoint: The Reporter can explain the full solution in under 60 seconds.

Challenge Zone

Extension: The cafeteria manager says she can get a 15% discount if she orders more than 30 lunches. If your combo feeds more than 30 students, calculate the new cost per lunch after the discount. How many MORE lunches could you serve with the same $142.50 budget?
What If? What if apple juice goes up to $1.35 per box? Would you keep it in your combo or swap it out? How does this change affect the total number of lunches?
Real-Life Connection: Think about a grocery store trip with your family. If you have $20 and need to buy items for dinner, how would you use decimal addition and division to plan your shopping list?

Defense Preparation

Questions Your Team Must Answer

  1. What is your combo, and what is the exact total cost? Show how you added the decimals.
  2. How many full lunches can the cafeteria serve? What does the remainder mean?
  3. How did you check that your addition and division are correct?
  4. Why did you choose this combo instead of a different one?
  5. If one price changed, how would it affect the number of lunches?

Sentence Starters for Your Defense

"We chose _____, _____, and _____ because their total of $_____ stays under the $4.75 limit."

"When we divided $142.50 by $_____, we got _____ full lunches with $_____ left over."

"We checked our work by multiplying _____ times $_____, which gave us $_____. Adding the remainder of $_____ gives us exactly $142.50."

"One mistake we caught was _____. We fixed it by _____."

Accuracy (4 pts) All decimal operations are correct; decimal points are aligned; no regrouping errors.
Model (4 pts) Place value chart is clear, labeled, and shows every step of the addition.
Reasoning (4 pts) Team explains why their combo is the best choice and what the remainder means.
Communication (4 pts) Reporter speaks clearly, uses math vocabulary, and every teammate can explain the solution.

Exit Product

Deliver: Cafeteria Budget Report

Your team submits a one-page report that includes:

  • Your combo items and each price listed
  • A place value addition chart showing the combo total
  • The division showing how many lunches and leftover money
  • A multiplication check proving the division is correct
  • A comparison with at least one other combo
  • A 3-sentence defense: claim, evidence, and reasonableness check

Self-Assessment

  • I lined up all decimal points before adding.
  • I checked my work with the inverse operation.
  • I can explain what the quotient and remainder mean in this situation.
  • I used math vocabulary (sum, product, quotient, remainder) in my defense.

Student Work Space

Combo Items and Prices:

Place Value Addition:

Division (Budget / Combo Cost):

Multiplication Check:

Defense (Claim, Evidence, Reasonableness):