Decimals 2B
Overview
This Phlow guides students through subtracting decimal numbers step by step, with a focus on correctly lining up decimal points and applying borrowing where needed. The worked example is 5 – 1.6.
- Choosing the correct setup: Students must identify the proper column layout, reinforcing the importance of lining up decimal points.
- Confirming the operation: They recognise the subtraction sign and confirm that the calculation is subtraction, not addition.
- Borrowing explained: Since 0 cannot subtract 6, a 1 is borrowed, changing 0 into 10. Students then calculate 10 – 6 = 4.
- Repaying the borrow: The reminder that the borrowed 1 must be returned changes the next step into 5 – 2, giving 3.
- Decimal placement: Finally, students identify the correct position of the decimal point in the answer.
By the end, learners see that 5.0 – 1.6 = 3.4. This exercise builds understanding of subtraction with decimals, reinforces place value, and gives practice in carrying out borrowing correctly.
Prerequisite Knowledge Required
- Decimals 2A – adding decimals and aligning place values.
- Subtract 1 / Subtract 2 – subtracting whole numbers with borrowing.
- Place Value 1A / 1B – understanding units and tenths.
Main Category
Number – Decimals and Place Value
Estimated Completion Time
Approx 6-10 seconds per question. 20 questions total. Total time: 2-4 minute.
Cognitive Load / Step Size
Moderate — introduces borrowing with decimals, which adds a small conceptual leap. Steps are well broken down to maintain manageability without confusion.
Language & Literacy Demand
Low — short, direct instructions (“Subtract 1.6 from 5”) supported by visual alignment of columns. Minimal reading complexity.
Clarity & Design
Strong — decimal points are clearly aligned and highlighted in each step. The borrow process is visualised numerically, showing the transition from 0 → 10.
Curriculum Alignment
Aligned with Number – Operations with Decimals strand of the Irish mathematics curriculum:
- Subtract decimal numbers with up to two decimal places.
- Apply borrowing (regrouping) correctly in decimal subtraction.
- Reinforce place value when subtracting across whole and decimal numbers.
Engagement & Motivation
Moderate to high — the step-by-step structure promotes understanding and builds confidence as students see how borrowing works visually.
Error Opportunities & Misconceptions
- Forgetting to align decimals.
- Ignoring the need to borrow when subtracting smaller from larger digits.
- Misplacing the decimal in the final answer.
Transferability / Real-World Anchoring
High — directly applies to real contexts like subtracting prices (€5.00 – €1.60) or measuring differences (5.0 m – 1.6 m).
Conceptual vs Procedural Balance
Balanced — procedural fluency (borrowing) supported by conceptual clarity about decimal placement and place value.
Learning Objectives Addressed
- Align decimal points correctly in subtraction problems.
- Apply borrowing when subtracting decimals that require regrouping.
- Maintain correct decimal placement in final answers.
- Strengthen understanding of place value between whole numbers and tenths.
What Your Score Says About You
- Less than 5: You may need to review how to align decimals and apply borrowing.
- Between 6–7: You understand subtraction but occasionally misplace decimals or skip a borrow.
- Between 8–9: You’re nearly fluent — just check your borrowing accuracy.
- 10/10: Excellent — you subtract decimals precisely and with full understanding of place value.