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Adding and subtracting fractions with unlike denominators

By OtisamLMS · 21 Oct 2026

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Subject
Core Mathematics · SHS
Year
SHS 1
Week
Term 1 · Week 4
Lessons
3 × 60 min
Class size
45
Strand
Number
Sub-strand
Fractions, decimals and percentages
Content standard
Learners carry out the four operations on fractions and use them to solve everyday problems.
Key words
numeratordenominatorequivalent fractionlowest common multiplemixed numberimproper fraction

Learning indicators

  • Find the lowest common multiple of two or three denominators
  • Add and subtract fractions and mixed numbers with unlike denominators
  • Check an answer by estimating with whole numbers

Core competencies

  • Critical thinking and problem solving
  • Communication and collaboration
  • Personal development (perseverance)

Resources

  • Paper strips (one A4 sheet per pair)
  • A market price list written on the board
  • Exercise books and coloured pens

Lesson flow

  1. 1Starter

    Write 1/2 + 1/3 on the board and ask three learners to give a quick guess. Most will say 2/5. Fold a paper strip into halves and another into thirds and hold them side by side: is 2/5 really bigger than 1/2? Let pairs argue for two minutes before you move on.

  2. 2Main activities

    1. Pairs fold strips into halves, thirds and sixths and shade 1/2 and 1/3 on the sixths strip. They record 1/2 = 3/6 and 1/3 = 2/6, so the sum is 5/6. 2. Ask: why did sixths work? Draw out that 6 is a multiple of both 2 and 3. Introduce the lowest common multiple and list multiples to find it for 4 and 6, then 3, 4 and 8. 3. Model two examples on the board, saying each step aloud: find the LCM, rewrite each fraction, add or subtract the numerators, simplify. 4. Mixed numbers: a trader sells 2 3/4 kg of rice in the morning and 1 2/3 kg in the afternoon. Groups solve it two ways (whole numbers first, then improper fractions) and compare. 5. Learners work through eight graded questions. Circulate, and pull a small group to the front table for extra modelling if needed.

  3. 3Reflection

    Learners write one sentence on a slip: 'The mistake I will not make again is…'. Read a few aloud. Close by returning to 1/2 + 1/3 and asking a learner to explain why 2/5 was wrong.

Assessment

Exit questions: (a) 3/4 + 1/6 (b) 5/8 − 1/3 (c) 3 1/2 − 1 4/5. A learner who gets (c) right has met all three indicators. Mark in class; note who needs support in the next lesson.

Differentiation

Support: keep the folded strips on the desk and limit the work to denominators below 12. Extension: write a word problem that needs 2/3 + 3/5 and swap it with a partner.

Homework

Find two prices at home or in the market that use halves or quarters (e.g. half a bag of gari) and write a subtraction problem from them.

Teacher notes

Learners often add the denominators. The paper strips in the starter are worth the time; do not skip them.
Fractions, decimals and percentages Core Mathematics practice questions Video lessons

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