Fractions (operations, mixed numbers) — KCSE Mathematics

KCSE Mathematics · 90 practice questions · 4 syllabus objectives · 4 revision lessons

35 easy34 medium21 hard

Last updated · Aligned to the KNEC KCSE syllabus

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Add, subtract, multiply and divide fractions and mixed numbers, expressing answers in their simplest form

Convert between improper fractions and mixed numbers; compare and order fractions on a number line

Apply operations on fractions to solve problems involving proportional sharing, ratios and rates

Fractions (operations, mixed numbers)

Revision Notes

Concise lesson notes for Fractions (operations, mixed numbers), written to the KCSE Mathematics marking standard. Read the first lesson free below.

Operations with Fractions and Mixed Numbers

To add or subtract fractions, ensure they have a common denominator. For example, to add (\frac{1}{4} + \frac{1}{2}), convert (\frac{1}{2}) to (\frac{2}{4}) so that both fractions have the same denominator. Thus, (\frac{1}{4} + \frac{2}{4} = \frac{3}{4}).

When multiplying fractions, simply multiply the numerators and the denominators. For example, (\frac{2}{3} \times \frac{3}{4} = \frac{2 \times 3}{3 \times 4} = \frac{6}{12} = \frac{1}{2}) in simplest form.

For division, multiply by the reciprocal. For example, (\frac{3}{4} \div \frac{2}{3} = \frac{3}{4} \times \frac{3}{2} = \frac{9}{8}), which can be expressed as the mixed number (1 \frac{1}{8}).

Always simplify your answers to their lowest terms.

Key points to remember

  • Find a common denominator for addition and subtraction.
  • Multiply numerators and denominators for multiplication.
  • Use the reciprocal for division of fractions.
  • Express answers in simplest form.
  • Convert improper fractions to mixed numbers when necessary.

Worked example

Add: (\frac{3}{5} + \frac{1}{10})
Convert (\frac{3}{5}) to (\frac{6}{10}): (\frac{6}{10} + \frac{1}{10} = \frac{7}{10}).

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More lessons in this topic

Lesson 2: Converting Improper Fractions and Mixed Numbers

Objective: Convert between improper fractions and mixed numbers; compare and order fractions on a number line

To convert between improper fractions and mixed numbers, follow these steps:

Improper Fraction to Mixed Number:

  1. Divide the numerator by the denominator.
  2. The quotient is the whole number.
  3. The remainder becomes the new numerator over the original denominator.

Mixed Number to Improper Fraction:

  1. Multiply the whole number by the denominator.
  2. Add the numerator to this product.
  3. Place the result over the original denominator.

Comparing and Ordering Fractions:
To compare fractions, convert them to a common denominator or convert them to decimal form.
You can also use a number line to visualize their positions.

For example, to order the fractions 1/2, 3/4, and 2/3, convert them to decimals:

  • 1/2 = 0.5
  • 3/4 = 0.75
  • 2/3 ≈ 0.67
    Thus, the order is: 1/2 < 2/3 < 3/4.
  • Improper fractions convert by dividing numerator by denominator.
  • Mixed numbers convert by multiplying and adding.
  • Common denominators help compare fractions.
  • Number lines visualize the order of fractions.
  • Decimals can simplify fraction comparison.

Convert 9/4 to a mixed number:

  • Divide 9 by 4, quotient is 2, remainder 1.
  • Thus, 9/4 = 2 1/4.
Lesson 3: Operations on Fractions for Sharing

Objective: Apply operations on fractions to solve problems involving proportional sharing, ratios and rates

To apply operations on fractions effectively, we must understand how to add, subtract, multiply, and divide fractions. Key steps include:

  • Finding a common denominator for addition and subtraction.
  • For multiplication, multiply the numerators and denominators directly.
  • For division, multiply by the reciprocal of the second fraction.

Example Problem:
If 3/4 of a cake is shared among 2 friends, how much does each friend receive?
Solution:

  1. Divide 3/4 by 2:
    • 3/4 ÷ 2 = 3/4 × 1/2 = 3/8.
  2. Each friend receives 3/8 of the cake.

Another Example:
A recipe requires 2/3 cup of sugar, but you want to make half the recipe. How much sugar do you need?
Solution:

  1. Multiply 2/3 by 1/2:
    • 2/3 × 1/2 = 2/6 = 1/3.
  2. You need 1/3 cup of sugar.
  • Find a common denominator for adding/subtracting fractions.
  • Multiply numerators and denominators directly for multiplication.
  • Use the reciprocal for division of fractions.
  • Carefully simplify fractions when possible.
  • Apply operations in real-life sharing scenarios.

If 1/2 of a pizza is left and you eat 1/4 of it, how much is left?
1/2 - 1/4 = 2/4 - 1/4 = 1/4.
You have 1/4 of the pizza left.

Lesson 4: Operations with Fractions and Mixed Numbers

Objective: Fractions (operations, mixed numbers)

Fractions and mixed numbers are essential in mathematics. To perform operations like addition, subtraction, multiplication, and division, follow these steps:

Addition and Subtraction:

  1. Ensure fractions have a common denominator.
  2. Add or subtract the numerators while keeping the denominator the same.
  3. Simplify if necessary.

Multiplication:

  1. Multiply the numerators together.
  2. Multiply the denominators together.
  3. Simplify the resulting fraction.

Division:

  1. Invert (flip) the second fraction.
  2. Multiply as per the multiplication rules.
  3. Simplify the result.

Mixed Numbers:

  • Convert mixed numbers to improper fractions before performing operations.
  • After calculations, convert back to mixed numbers if needed.

For example, to add 1 1/2 + 2 2/3:

  1. Convert to improper fractions: 1 1/2 = 3/2 and 2 2/3 = 8/3.
  2. Find a common denominator (6): 3/2 = 9/6 and 8/3 = 16/6.
  3. Add: 9/6 + 16/6 = 25/6 = 4 1/6 (mixed number).
  • Add/subtract fractions with a common denominator.
  • Multiply fractions by multiplying numerators and denominators.
  • Divide fractions by multiplying by the reciprocal.
  • Convert mixed numbers to improper fractions for operations.
  • Simplify fractions and mixed numbers when necessary.

Add 1/4 + 3/8.

  1. Convert 1/4 to 2/8.
  2. 2/8 + 3/8 = 5/8.

Sample Questions

Read 3 questions and answers free. Sign up to access all 90 questions with full KNEC-style marking schemes and a personalised study plan.

1
easySHORT ANSWER3 marks

A shop sells 3/4 of a box of chocolates. If a customer buys 1/2 of what is left in the box, what fraction of the original box of chocolates does the customer buy? (3 marks)

Answer & marking scheme

Part (a) — 3 marks
Calculate remaining chocolates: 1 - 3/4 = 1/4 (1 mk)
Calculate amount bought by customer: 1/2 × 1/4 = 1/8 (1 mk)
Identify that the customer bought 1/8 of the original box (1 mk)
2
easySHORT ANSWER3 marks

State which of the two fractions 4/7 and 3/5 is larger and explain your reasoning. (3 marks)

Answer & marking scheme

Part (a) — 3 marks
Convert both fractions to have a common denominator, which is 35 (1 mk)
Rewrite 4/7 as 20/35 and 3/5 as 21/35 (1 mk)
State that 21/35 is larger than 20/35, thus 3/5 is larger than 4/7 (1 mk)
3
easySHORT ANSWER3 marks

Evaluate: 3/4 × 2/5 ÷ 1/2, giving your answer as a fraction in simplest form. (3 marks)

Answer & marking scheme

Part (b) — 3 marks
Multiply 3/4 by 2/5: 3/4 × 2/5 = 6/20 (1 mk)
Divide by 1/2: 6/20 ÷ 1/2 = 6/20 × 2/1 = 12/20 (1 mk)
Simplify 12/20 to 3/5 (1 mk)
4

Calculate the value of 2⅓ + 1⅔ - 1/2, expressing your answer as a mixed number in its simplest form. (3 marks)

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Frequently asked questions

What does the KCSE Mathematics topic "Fractions (operations, mixed numbers)" cover?

Fractions (operations, mixed numbers) covers Add, subtract, multiply and divide fractions and mixed numbers, expressing answers in their simplest form; Convert between improper fractions and mixed numbers; compare and order fractions on a number line; Apply operations on fractions to solve problems involving proportional sharing, ratios and rates, and more, all aligned to the official KNEC KCSE Mathematics syllabus.

How many practice questions are available for Fractions (operations, mixed numbers)?

HighMarks has 90 Fractions (operations, mixed numbers) practice questions for KCSE Mathematics, each with a full marking scheme. The first 3 are free; sign up to access the rest, plus all KCSE mock exams and past papers.

Are these aligned with the KNEC KCSE syllabus?

Yes. Every objective on this page is taken directly from the official KNEC KCSE Mathematics syllabus. Practice questions match the KCSE exam format and are graded against the standard KNEC marking scheme.

How should I revise Fractions (operations, mixed numbers) for the KCSE exam?

Start with the revision notes on this page to refresh the core concepts, then work through the practice questions in increasing difficulty. Sign up for HighMarks to get a personalised study plan that adapts to the topics you keep getting wrong, plus mock exams, subject-wide practice, and detailed performance tracking. See pricing.

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