6.NOS.3 Lesson 2-11-group1 🟡 Group 1 · Set B
MASTERY CHECK
☐ Exceeds☐ Meets Target☐ Needs Practice

2.11 Small Group · Group 1

Second Practice Form · Re-Teach, Homework or Retake · Same Standard, New Problems

Visual Models · Add and Subtract Decimals · Decimal · Procedural Fluency

Interactive Workbench & Models →
Name: Date: Period: Learning Goal:
■ CONCEPT SUMMARY & GUIDED NOTES: Let's build it together — How do you add and subtract decimals?
1Line up the decimal points, add zeros so each number has the same number of decimal places, then add or subtract one column at a time.
  • A decimal is a number with a point that shows parts smaller than one whole. To add or subtract decimals, you line up the decimal points so the same place values match. We'll walk through a worked example, try one together, then you'll try a few with hints right there when you need them.
2Worked Example — Watch me
  1. The tank has 128.75 liters. A shuttle adds 46.8 liters. I line up the decimal points and annex a zero: 46.80.
  2. I add: 128.75 + 46.80 = 175.55 liters.
  3. Now the thrusters use 19.35 liters, so I subtract: 175.55 − 19.35 = 156.20.
  4. The final fuel level is 156.20 liters. I check with estimation: about 130 + 47 − 19 = 158, which is close, so my answer is reasonable.
3Mathematical Word Bank
  • Add and Subtract Decimals (Sumar y restar decimales) — Combine or find the difference between decimals by lining up equal place values.
  • Decimal (Decimal) — A number with a dot, like 0.5, that shows a part less than one.
  • Place value (Valor posicional) — What a digit is worth based on where it sits in a number.
  • Tenths (Décimas) — The first spot after the decimal point. It shows parts out of 10.
  • Hundredths (Centésimas) — The second spot after the decimal point. It shows parts out of 100.
  • Annex zeros (Agregar ceros) — Adding zeros at the end of a decimal so numbers line up evenly.
4Watch out
  • A common mistake in Add and Subtract Decimals is lining up the last digits (the right edges) of each number instead of lining up the decimal points — for example, adding 8.3 and 2.45 as if the 3 and the 5 belong in the same column. Before you add or subtract, add zeros so every number has the same number of decimal places (write 8.3 as 8.30), then check that the decimal points sit directly above one another.
SECTION 1 REAL-WORLD CONTEXTS & PROBLEM SOLVING [Applications]
  1. 1 MULTIPLE CHOICE

    A student buys items costing $4.59, $12.75, and $3.80. What is the total cost?

    1. A$21.14
    2. B$20.14
    3. C$21.04
    4. D$21.24
    ✏️ Workspace & Solution Steps
  2. 2 MULTIPLE CHOICE

    Case File: A crew member's snack receipt shows $27.60 for dried fruit and $15.45 for protein bars. What is the total on the receipt?

    1. A$43.05
    2. B$42.05
    3. C$43.15
    4. D$42.95
    ✏️ Workspace & Solution Steps
  3. 3 MULTIPLE CHOICE

    Case File: The oxygen gauge dropped from 9.6 units to a new reading after the crew used 4.75 units. How much oxygen is left?

    1. A4.85
    2. B5.85
    3. C4.95
    4. D5.15
    ✏️ Workspace & Solution Steps
  4. 4 MULTIPLE CHOICE

    Case File: A supply log started the shift with $48.00 in the station snack fund. By the end, $31.27 had been spent. How much is left in the fund?

    1. A$16.73
    2. B$17.73
    3. C$16.83
    4. D$17.27
    ✏️ Workspace & Solution Steps
SECTION 2 MATHEMATICAL WRITING & ERROR ANALYSIS [Reasoning & Critique]
  1. 5 ERROR ANALYSIS

    Spot the Mistake — Missing Annex Zero

    1. 1Problem:Add 8.3 + 2.45
    2. 2Set up:Lined up the right edges so the 3 sits under the 5
    3. 3Add:8.3 + 2.45 = 8.75
    4. 4Final answer:8.75

    Which step contains the error? Explain the mathematical misconception and write the correct calculation below.

    ✏️ Corrected Mathematical Work & Explanation
  2. 6 ERROR ANALYSIS

    Spot the Mistake — Subtracting Without a Placeholder

    1. 1Problem:Subtract 12.5 − 3.45
    2. 2Set up:Left 12.5 as one decimal place instead of annexing a zero
    3. 3Subtract:12.5 − 3.45 = 9.5
    4. 4Final answer:9.5

    Which step contains the error? Explain the mathematical misconception and write the correct calculation below.

    ✏️ Corrected Mathematical Work & Explanation
📐 CER MATHEMATICAL PROOF MATRIX (CER 2.0) SMP.3 / Proof & Justification

Writing Task: Justify why your mathematical solution is accurate and complete.

C Claim
Starter: My mathematical claim is that the solution is...
E Evidence
Starter: The evidence from the model/table demonstrates that...
R Reasoning
Starter: This proves my answer because the standard mathematical definition of...
Student Mastery Self-Assessment:
1 · Need More Support
2 · Getting Closer
3 · Got It / Solid
4 · Master / Can Teach It