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Math lesson plan · 11th grade (Year 12 in England) · 45 minutes

Add and subtract algebraic fractions

Algebra

CCSS HSA.APR.D.7England: GCSE Higher Algebra

Objective and success criteria

Students will: Add and subtract algebraic fractions.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Algebraic fractions

Leads to: the next skill in this area.

Materials: Balance scales or a balance drawing, Algebra tiles, Function machine cards, Mini whiteboards and pens, Printed student sheet (below).

Warm-up · 5 min

  • Quick retrieval from earlier learning (Algebraic fractions). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Simplify: (x² − 1) / (x + 1) (x + 1 / x − 1 / x) → x − 1Prompt: Factorise the numerator first.
  2. Write as a single fraction: 2/(x + 3) + 5/(x + 2). Type the numerator over the factorised denominator, e.g. (3x+5)/((x+1)(x+2)). → (7x+19)/((x+3)(x+2))Prompt: The common denominator is the product of the two brackets.
  3. Simplify: (x² − 5x + 4) / (x − 4) (x + 1 / x − 1 / x + 4 / x − 5) → x − 1Prompt: Factorise the numerator first.

Hook · 5 min

  • Show a "think of a number" puzzle and ask the class to work out the starting number.
  • Share the objective: Add and subtract algebraic fractions. Read the success criteria together.

I do: model it · 10 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: Write as a single fraction: 4/(x − 2) + 4/(x + 1)
  • Step 1: (4(x + 1) + 4(x − 2))/((x − 2)(x + 1))
  • Step 2: (8x − 4)/((x − 2)(x + 1))
  • Answer: (8x − 4)/((x − 2)(x + 1))
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 10 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. Write as a single fraction: 5/(x + 5) + 4/(x + 2) ((9x + 30)/((x + 5)(x + 2)) / (9x − 10)/((x + 5)(x + 2)) / 9/((x + 5)(x + 2)) / (9x + 30)/((x + 5) + (x + 2))) → (9x + 30)/((x + 5)(x + 2))Prompt: Use the common denominator (x + 5)(x + 2).
  2. Simplify: 5/(x + 5) + (x − 5)/(x² − 25) (6/(x − 5) / 6/(x + 5) / 6/(x² − 25) / 5/(x + 5)) → 6/(x + 5)Prompt: Factorise x² − 25 first.

You do: independent practice · 10 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 5 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. Write as a single fraction: 5/(x + 2) − 4/(x + 4) ((x + 28)/((x + 2)(x + 4)) / (x + 12)/((x + 2)(x + 4)) / (x + 12)/((x + 2) + (x + 4)) / 1/((x + 2)(x + 4))) → (x + 12)/((x + 2)(x + 4))Prompt: Use the common denominator (x + 2)(x + 4).
  2. Simplify: 6/(x + 2) + (x − 2)/(x² − 4) (6/(x + 2) / 7/(x + 2) / (x − 8)/(x² − 4) / 7/(x − 2)) → 7/(x + 2)Prompt: Factorise x² − 4 first.

Watch out for

  • Doing an operation to one side of an equation but not the other.
  • Reading 3x as 3 + x, or thinking x always stands for one particular number.

Support and stretch

Support

  • Review first: Algebraic fractions.
  • Use concrete materials: balance scales or a balance drawing.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-11.

Free lesson plan from eurekami.com/lesson-plan-builder

eurekami

Add and subtract algebraic fractions

Name

Date

Score/ 8

  1. Question 1

    Simplify: 5/(x + 6) + (x − 6)/(x² − 36)

    • A. 6/(x + 6)
    • B. 6/(x − 6)
    • C. 6/(x² − 36)
    • D. (x − 11)/(x² − 36)

  2. Question 2

    Write as a single fraction: 3/(x + 3) + 2/(x + 5)

    • A. (5x + 9)/((x + 3)(x + 5))
    • B. 5/((x + 3)(x + 5))
    • C. (5x + 21)/((x + 3)(x + 5))
    • D. (5x + 21)/((x + 3) + (x + 5))

  3. Question 3

    Simplify: 3/(x + 6) + (x − 6)/(x² − 36)

    • A. 4/(x² − 36)
    • B. (x − 9)/(x² − 36)
    • C. 4/(x + 6)
    • D. 4/(x − 6)

  4. Question 4

    Write as a single fraction: 3/(x − 6) − 4/(x − 2)

    • A. (−x − 30)/((x − 6)(x − 2))
    • B. (−x + 18)/((x − 6) + (x − 2))
    • C. -1/((x − 6)(x − 2))
    • D. (−x + 18)/((x − 6)(x − 2))

  5. Question 5

    Simplify: 3/(x + 7) + (x − 7)/(x² − 49)

    • A. 4/(x² − 49)
    • B. (x − 10)/(x² − 49)
    • C. 4/(x − 7)
    • D. 4/(x + 7)

  6. Question 6

    Write as a single fraction: 3/(x + 6) − 1/(x − 2)

    • A. (2x − 12)/((x + 6)(x − 2))
    • B. (2x)/((x + 6)(x − 2))
    • C. 2/((x + 6)(x − 2))
    • D. (2x − 12)/((x + 6) + (x − 2))

  7. Question 7

    Simplify: 2/(x + 5) + (x − 5)/(x² − 25)

    • A. (x − 7)/(x² − 25)
    • B. 3/(x + 5)
    • C. 2/(x + 5)
    • D. 3/(x − 5)

  8. Question 8

    Write as a single fraction: 4/(x + 2) + 3/(x − 5)

    • A. (7x − 14)/((x + 2) + (x − 5))
    • B. 7/((x + 2)(x − 5))
    • C. (7x − 26)/((x + 2)(x − 5))
    • D. (7x − 14)/((x + 2)(x − 5))

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Answer key: Add and subtract algebraic fractions

  1. 1. A. 6/(x + 6)

  2. 2. C. (5x + 21)/((x + 3)(x + 5))

  3. 3. C. 4/(x + 6)

  4. 4. D. (−x + 18)/((x − 6)(x − 2))

  5. 5. D. 4/(x + 7)

  6. 6. A. (2x − 12)/((x + 6)(x − 2))

  7. 7. B. 3/(x + 5)

  8. 8. D. (7x − 14)/((x + 2)(x − 5))