Number: Fractions · B5 Mathematics

Lesson notes

Learning Objectives

Indicator: B5.1.3.1.4 - Use the concept of equivalent fractions for addition and subtraction of fractions greater than one (improper or mixed fractions)

By the end of the lesson, learners can:

Add like mixed fractions greater than 1 by adding the whole numbers and the fractional parts separately.
Subtract like mixed fractions greater than 1 by converting them to improper fractions and subtracting the numerators.
Find the Lowest Common Denominator (LCD) of two different denominators and express mixed fractions as equivalent fractions with that common denominator.
Add and subtract mixed fractions with different denominators using the LCD method, simplifying answers where possible.
Solve real-life word problems involving the addition and subtraction of mixed fractions.

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Curriculum details

Strand: Number (Strand 1)
Sub-strand: Number: Fractions (1.3)
Content standard: B5.1.3.1 - Demonstrate understanding of strategies for comparing, adding, subtracting and multiplying fractions
Indicator: B5.1.3.1.4 - Use the concept of equivalent fractions for addition and subtraction of fractions greater than one (improper or mixed fractions)
Suggested placement: Term 2, Week 1 (Week 13 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.
Source document note: The official curriculum document has a fault in this entry, so the curriculum text above is transcribed exactly as printed:

exemplars - p.73
Curriculum reference: Mathematics Curriculum for Primary Schools (Basic 4-6), 2019, p. 73
Transcribed from the official NaCCA publication. Check this page against the source.

Exemplars (from the NaCCA curriculum)

E.g. 1 To add like mixed fractions that are larger than 1, i.e. 2 1/3 and 3 2/3, we write down the sum of the whole numbers and add the fractions; i.e. 2 1/3 + 3 2/3 = 5 + 1/3 + 2/3, = 5 1+2/3 = 5 3/3 = 6.
E.g. 2 To subtract like-fractions that are larger than 1, i.e. 2 1/3 and 3 2/3, we change the mixed fractions into improper fractions and subtract; i.e. 3 2/3 - 2 1/3 = 11/3 - 7/3 = 11-7/3 = 4/3 = 1 1/3
E.g. 3 To add or subtract improper fractions with different denominators, (2 1/3 and 3 2/5) we need find the Lowest Common Denominator (LCD) and use this to express the equivalent fractions. The LCD is 15 and the equivalent fractions are 2 5/15 and 3 6/15; their sum is 2 1/3 + 3 2/5 = 2 5/15 + 3 6/15 = 5 5+6/15 which is 5 11/15; and difference 3 2/5 - 2 1/3 = 1 6-5/15 = 1 1/15 Every fraction on this page is stacked and its parts interleave with the sentence in the text layer; they are written here inline. A reviewer should check each fraction against the page.