Number Operations · B4 Mathematics

Lesson notes

Learning Objectives

Indicator: B4.1.2.2.2 - Apply mental mathematics strategies for multiplication, such as annexing then adding zero halving and doubling using the distributive property

By the end of the lesson, learners can:

Determine products where one factor is a multiple of 10, 100, or 1000 by annexing zeros correctly (e.g., 3 × 200 = 600).
Apply the halving and doubling strategy to find products mentally (e.g., 32 × 5 = 16 × 10 = 160).
Use the distributive property to multiply factors close to multiples of 10 (e.g., 29 × 7 = 203).
Explain which mental strategy is most efficient for a given multiplication problem and justify their choice.
Solve word problems involving these strategies in everyday contexts.

This lesson builds directly on the basic facts learners mastered in Week 9 (facts up to 12 × 12 and related strategies) and prepares them for efficient multiplication of multi-digit numbers in the next slot (B4.1.2.3.1).

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Curriculum details

Strand: Number (Strand 1)
Sub-strand: Number Operations (1.2)
Content standard: B4.1.2.2 - Describe and apply mental mathematics strategies and number properties to determine answers for basic multiplication facts to 81 and related division facts
Indicator: B4.1.2.2.2 - Apply mental mathematics strategies for multiplication, such as annexing then adding zero halving and doubling using the distributive property
Suggested placement: Term 1, Week 10 (Week 10 of the year)
Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.
Curriculum reference: Mathematics Curriculum for Primary Schools (Basic 4-6), 2019, p. 16
Transcribed from the official NaCCA publication. Check this page against the source.

Exemplars (from the NaCCA curriculum)

E.g. 1 Determine the products when one factor is a multiple of 10, 100, or 1000 by annexing zero or adding zeros (e.g., for 3×200 think of 3×2 and then add two zeros)
E.g. 2 Apply halving and doubling when determining a given product (e.g., 32×5 is the same as 16×10)
E.g. 3 Apply the distributive property to determine a given product involving multiplying factors that are close to multiples of 10 (e.g., 29×7 = (30×7) - (1×7) = 203