Add & Sub 3
Overview
Builds fluency with basic number operations by focusing on missing-number problems — equations where one part is hidden, and the student must work it out logically.
Addition
The sequence begins with addition: Example 1: “Is it 1 plus or minus 1 that equals 2?” Students must choose the correct operation symbol (+ or −), learning that 1 + 1 = 2.
Subtraction (Unknown at the Start)
Example 2: “What minus 5 equals 4?” Learners must think inversely, recognising that 9 − 5 = 4, and selecting 9 as the missing number.
Subtraction (Unknown in the Middle)
Example 3: “8 minus what equals 5?” Here, students identify 3 as the missing value, understanding subtraction as finding the difference.
This step-by-step progression teaches the structure of equations and reinforces the relationship between addition and subtraction. By alternating question formats and positions of the missing number, students practise flexible problem-solving rather than memorising single patterns.
Prerequisite Knowledge Required
- Linked Phlows: Add 1 – adding small numbers.
- Sub 1 – subtracting small numbers.
- Equals 2 – understanding equality and balance in equations.
- Add & Sub 2 – introduction to addition/subtraction pairs.
Main Category
Arithmetic – Addition & Subtraction
Estimated Completion Time
Approx 6–10 seconds per question. 20 questions total. Total time: 2–4 minutes.
Cognitive Load / Step Size
Moderate — the visual simplicity and small numbers reduce load, but introducing the missing-number position (start, middle, or operation) increases cognitive demand slightly, supporting reasoning development.
Language & Literacy Demand
Low — key words like plus, minus, and equals are consistently colour-highlighted. Sentences are short and pattern-based, aiding comprehension for early readers.
Clarity & Design
Excellent — strong visual contrast between numbers and operation symbols. The purple question box clearly signals the missing value. Green and grey buttons provide instant feedback without distraction.
Curriculum Alignment
Irish Curriculum Strand: Number – Operations: Addition and Subtraction
- Use inverse relationships between addition and subtraction.
- Find missing numbers in number sentences.
- Understand the role of the equals sign as balance.
- Apply logical reasoning to solve basic equations.
Engagement & Motivation
High — the “fill in the blank” format feels like a puzzle. Immediate success on small problems builds confidence and encourages learners to spot patterns between operations.
Error Opportunities & Misconceptions
- Confusing when to add vs. subtract.
- Misreading the equals sign as “next step” instead of “same value.”
- Forgetting that subtraction can be used to find an unknown addend.
Visual feedback and consistent sentence structure address these common errors effectively.
Transferability / Real-World Anchoring
Moderate — builds arithmetic reasoning essential for later algebra, budgeting, time calculation, and measurement problems. Understanding how operations undo each other supports flexible problem-solving.
Conceptual vs Procedural Balance
Conceptual — learners explore relationships between operations and positions of unknowns rather than performing rote calculations.
Learning Objectives Addressed
- Recognise the relationship between addition and subtraction.
- Identify missing values in simple equations.
- Strengthen understanding of the equals sign.
- Apply logical reasoning to basic number sentences.
What Your Score Says About You
- Less than 15: Still developing awareness of how addition and subtraction connect.
- 16–22: Understands direction of operations but may misplace the missing number.
- 23–29: Solves most missing-number problems confidently.
- 30 / 30: Excellent mastery — understands and applies inverse relationships in all equation formats.