Learn on PengiSaxon Math, Course 2Chapter 3: Lessons 21-30, Investigation 3

Lesson 24: Reducing Fractions, Part 2

In this Grade 7 Saxon Math Course 2 lesson, students learn to reduce fractions using prime factorization and to find the greatest common factor of two numbers. The lesson also introduces canceling, a technique for reducing fractions before multiplying by pairing any numerator with any denominator across two or more fractions. These methods are applied to increasingly complex fraction multiplication problems to simplify calculations efficiently.

Section 1

πŸ“˜ Reducing Fractions, Part 2

New Concept

Instead of reducing a fraction after multiplying, we can reduce before we multiply. This process, also known as canceling, works by pairing any numerator with any denominator to divide out common factors.

What’s next

Next, we'll walk through several examples, including how to use prime factorization to find common factors and how to cancel across multiple fractions at once.

Section 2

Using prime factorization to reduce

Property

To reduce a fraction using prime factorization, rewrite the numerator and the denominator as products of their prime factors. Then, identify and cancel out pairs of common prime factors that form a fraction equal to 1.

Examples

4201050=2β‹…2β‹…3β‹…5β‹…72β‹…3β‹…5β‹…5β‹…7=2β‹…2β‹…3β‹…5β‹…72β‹…3β‹…5β‹…5β‹…7=25\frac{420}{1050} = \frac{2 \cdot 2 \cdot 3 \cdot 5 \cdot 7}{2 \cdot 3 \cdot 5 \cdot 5 \cdot 7} = \frac{\cancel{2} \cdot 2 \cdot \cancel{3} \cdot \cancel{5} \cdot \cancel{7}}{\cancel{2} \cdot \cancel{3} \cdot 5 \cdot \cancel{5} \cdot \cancel{7}} = \frac{2}{5}
48144=2β‹…2β‹…2β‹…2β‹…32β‹…2β‹…2β‹…2β‹…3β‹…3=2β‹…2β‹…2β‹…2β‹…32β‹…2β‹…2β‹…2β‹…3β‹…3=13\frac{48}{144} = \frac{2 \cdot 2 \cdot 2 \cdot 2 \cdot 3}{2 \cdot 2 \cdot 2 \cdot 2 \cdot 3 \cdot 3} = \frac{\cancel{2 \cdot 2 \cdot 2 \cdot 2 \cdot 3}}{\cancel{2 \cdot 2 \cdot 2 \cdot 2 \cdot 3} \cdot 3} = \frac{1}{3}
626=2β‹…32β‹…13=2β‹…32β‹…13=313\frac{6}{26} = \frac{2 \cdot 3}{2 \cdot 13} = \frac{\cancel{2} \cdot 3}{\cancel{2} \cdot 13} = \frac{3}{13}

Explanation

Think of this as a matching game for numbers! By breaking down big numbers into their prime building blocks, you can easily spot the common parts and remove them. This method guarantees you'll find the simplest form of a fraction without any guesswork, turning a monster fraction into a mini one.

Section 3

Greatest common factor

Property

The greatest common factor (GCF) of two numbers is the greatest whole number that divides both numbers evenly. It can be found by identifying all the common prime factors of the two numbers and multiplying them together.

Examples

FactorsΒ ofΒ 420Β areΒ 2,2,3,5,7;Β FactorsΒ ofΒ 1050Β areΒ 2,3,5,5,7.Β GCFΒ isΒ 2β‹…3β‹…5β‹…7=210.\text{Factors of 420 are } 2, 2, 3, 5, 7; \text{ Factors of 1050 are } 2, 3, 5, 5, 7. \text{ GCF is } 2 \cdot 3 \cdot 5 \cdot 7 = 210.
FactorsΒ ofΒ 90Β areΒ 2,3,3,5;Β FactorsΒ ofΒ 324Β areΒ 2,2,3,3,3,3.Β GCFΒ isΒ 2β‹…3β‹…3=18.\text{Factors of 90 are } 2, 3, 3, 5; \text{ Factors of 324 are } 2, 2, 3, 3, 3, 3. \text{ GCF is } 2 \cdot 3 \cdot 3 = 18.
FactorsΒ ofΒ 540Β areΒ 2,2,3,3,3,5;Β FactorsΒ ofΒ 600Β areΒ 2,2,2,3,5,5.Β GCFΒ isΒ 2β‹…2β‹…3β‹…5=60.\text{Factors of 540 are } 2, 2, 3, 3, 3, 5; \text{ Factors of 600 are } 2, 2, 2, 3, 5, 5. \text{ GCF is } 2 \cdot 2 \cdot 3 \cdot 5 = 60.

Explanation

Meet the GCF, the biggest boss factor two numbers have in common! Using prime factorization, just find all the prime team members shared by both numbers and multiply them. This single 'boss factor' can then simplify a fraction in one clean shot, making your life way easier.

Section 4

Reducing before multiplying

Property

When multiplying fractions, you can simplify the problem by pairing any numerator with any denominator and dividing both by a common factor. This method is also known as canceling.

Examples

916β‹…23=93168β‹…2131=38\frac{9}{16} \cdot \frac{2}{3} = \frac{\stackrel{3}{\cancel{9}}}{\underset{8}{\cancel{16}}} \cdot \frac{\stackrel{1}{\cancel{2}}}{\underset{1}{\cancel{3}}} = \frac{3}{8}
89β‹…310β‹…54=8193β‹…31101β‹…5141=13\frac{8}{9} \cdot \frac{3}{10} \cdot \frac{5}{4} = \frac{\stackrel{1}{\cancel{8}}}{\underset{3}{\cancel{9}}} \cdot \frac{\stackrel{1}{\cancel{3}}}{\underset{1}{\cancel{10}}} \cdot \frac{\stackrel{1}{\cancel{5}}}{\underset{1}{\cancel{4}}} = \frac{1}{3}
58β‹…310=518β‹…3102=316\frac{5}{8} \cdot \frac{3}{10} = \frac{\stackrel{1}{\cancel{5}}}{8} \cdot \frac{3}{\underset{2}{\cancel{10}}} = \frac{3}{16}

Explanation

Why do the hard work after you multiply? Canceling lets you shrink the numbers before you multiply, making the whole problem simpler. It's like tidying up as you go! Find a numerator-denominator pair with a common factor, reduce them, and cruise to the right answer with smaller, friendlier numbers.

Book overview

Jump across lessons in the current chapter without opening the full course modal.

Continue this chapter

Chapter 3: Lessons 21-30, Investigation 3

  1. Lesson 1

    Lesson 21: Prime and Composite Numbers, Prime Factorization

  2. Lesson 2

    Lesson 22: Problems About a Fraction of a Group

  3. Lesson 3

    Lesson 23: Subtracting Mixed Numbers with Regrouping

  4. Lesson 4Current

    Lesson 24: Reducing Fractions, Part 2

  5. Lesson 5

    Lesson 25: Dividing Fractions

  6. Lesson 6

    Lesson 26: Multiplying and Dividing Mixed Numbers

  7. Lesson 7

    Lesson 27: Multiples, Least Common Multiple, Equivalent Division Problems

  8. Lesson 8

    Lesson 28: Two-Step Word Problems, Average, Part 1

  9. Lesson 9

    Lesson 29: Rounding Whole Numbers, Rounding Mixed Numbers, Estimating Answers

  10. Lesson 10

    Lesson 30: Common Denominators, Adding and Subtracting Fractions with Different Denominators

  11. Lesson 11

    Investigation 3: Coordinate Plane

Lesson overview

Expand to review the lesson summary and core properties.

Expand

Section 1

πŸ“˜ Reducing Fractions, Part 2

New Concept

Instead of reducing a fraction after multiplying, we can reduce before we multiply. This process, also known as canceling, works by pairing any numerator with any denominator to divide out common factors.

What’s next

Next, we'll walk through several examples, including how to use prime factorization to find common factors and how to cancel across multiple fractions at once.

Section 2

Using prime factorization to reduce

Property

To reduce a fraction using prime factorization, rewrite the numerator and the denominator as products of their prime factors. Then, identify and cancel out pairs of common prime factors that form a fraction equal to 1.

Examples

4201050=2β‹…2β‹…3β‹…5β‹…72β‹…3β‹…5β‹…5β‹…7=2β‹…2β‹…3β‹…5β‹…72β‹…3β‹…5β‹…5β‹…7=25\frac{420}{1050} = \frac{2 \cdot 2 \cdot 3 \cdot 5 \cdot 7}{2 \cdot 3 \cdot 5 \cdot 5 \cdot 7} = \frac{\cancel{2} \cdot 2 \cdot \cancel{3} \cdot \cancel{5} \cdot \cancel{7}}{\cancel{2} \cdot \cancel{3} \cdot 5 \cdot \cancel{5} \cdot \cancel{7}} = \frac{2}{5}
48144=2β‹…2β‹…2β‹…2β‹…32β‹…2β‹…2β‹…2β‹…3β‹…3=2β‹…2β‹…2β‹…2β‹…32β‹…2β‹…2β‹…2β‹…3β‹…3=13\frac{48}{144} = \frac{2 \cdot 2 \cdot 2 \cdot 2 \cdot 3}{2 \cdot 2 \cdot 2 \cdot 2 \cdot 3 \cdot 3} = \frac{\cancel{2 \cdot 2 \cdot 2 \cdot 2 \cdot 3}}{\cancel{2 \cdot 2 \cdot 2 \cdot 2 \cdot 3} \cdot 3} = \frac{1}{3}
626=2β‹…32β‹…13=2β‹…32β‹…13=313\frac{6}{26} = \frac{2 \cdot 3}{2 \cdot 13} = \frac{\cancel{2} \cdot 3}{\cancel{2} \cdot 13} = \frac{3}{13}

Explanation

Think of this as a matching game for numbers! By breaking down big numbers into their prime building blocks, you can easily spot the common parts and remove them. This method guarantees you'll find the simplest form of a fraction without any guesswork, turning a monster fraction into a mini one.

Section 3

Greatest common factor

Property

The greatest common factor (GCF) of two numbers is the greatest whole number that divides both numbers evenly. It can be found by identifying all the common prime factors of the two numbers and multiplying them together.

Examples

FactorsΒ ofΒ 420Β areΒ 2,2,3,5,7;Β FactorsΒ ofΒ 1050Β areΒ 2,3,5,5,7.Β GCFΒ isΒ 2β‹…3β‹…5β‹…7=210.\text{Factors of 420 are } 2, 2, 3, 5, 7; \text{ Factors of 1050 are } 2, 3, 5, 5, 7. \text{ GCF is } 2 \cdot 3 \cdot 5 \cdot 7 = 210.
FactorsΒ ofΒ 90Β areΒ 2,3,3,5;Β FactorsΒ ofΒ 324Β areΒ 2,2,3,3,3,3.Β GCFΒ isΒ 2β‹…3β‹…3=18.\text{Factors of 90 are } 2, 3, 3, 5; \text{ Factors of 324 are } 2, 2, 3, 3, 3, 3. \text{ GCF is } 2 \cdot 3 \cdot 3 = 18.
FactorsΒ ofΒ 540Β areΒ 2,2,3,3,3,5;Β FactorsΒ ofΒ 600Β areΒ 2,2,2,3,5,5.Β GCFΒ isΒ 2β‹…2β‹…3β‹…5=60.\text{Factors of 540 are } 2, 2, 3, 3, 3, 5; \text{ Factors of 600 are } 2, 2, 2, 3, 5, 5. \text{ GCF is } 2 \cdot 2 \cdot 3 \cdot 5 = 60.

Explanation

Meet the GCF, the biggest boss factor two numbers have in common! Using prime factorization, just find all the prime team members shared by both numbers and multiply them. This single 'boss factor' can then simplify a fraction in one clean shot, making your life way easier.

Section 4

Reducing before multiplying

Property

When multiplying fractions, you can simplify the problem by pairing any numerator with any denominator and dividing both by a common factor. This method is also known as canceling.

Examples

916β‹…23=93168β‹…2131=38\frac{9}{16} \cdot \frac{2}{3} = \frac{\stackrel{3}{\cancel{9}}}{\underset{8}{\cancel{16}}} \cdot \frac{\stackrel{1}{\cancel{2}}}{\underset{1}{\cancel{3}}} = \frac{3}{8}
89β‹…310β‹…54=8193β‹…31101β‹…5141=13\frac{8}{9} \cdot \frac{3}{10} \cdot \frac{5}{4} = \frac{\stackrel{1}{\cancel{8}}}{\underset{3}{\cancel{9}}} \cdot \frac{\stackrel{1}{\cancel{3}}}{\underset{1}{\cancel{10}}} \cdot \frac{\stackrel{1}{\cancel{5}}}{\underset{1}{\cancel{4}}} = \frac{1}{3}
58β‹…310=518β‹…3102=316\frac{5}{8} \cdot \frac{3}{10} = \frac{\stackrel{1}{\cancel{5}}}{8} \cdot \frac{3}{\underset{2}{\cancel{10}}} = \frac{3}{16}

Explanation

Why do the hard work after you multiply? Canceling lets you shrink the numbers before you multiply, making the whole problem simpler. It's like tidying up as you go! Find a numerator-denominator pair with a common factor, reduce them, and cruise to the right answer with smaller, friendlier numbers.

Book overview

Jump across lessons in the current chapter without opening the full course modal.

Continue this chapter

Chapter 3: Lessons 21-30, Investigation 3

  1. Lesson 1

    Lesson 21: Prime and Composite Numbers, Prime Factorization

  2. Lesson 2

    Lesson 22: Problems About a Fraction of a Group

  3. Lesson 3

    Lesson 23: Subtracting Mixed Numbers with Regrouping

  4. Lesson 4Current

    Lesson 24: Reducing Fractions, Part 2

  5. Lesson 5

    Lesson 25: Dividing Fractions

  6. Lesson 6

    Lesson 26: Multiplying and Dividing Mixed Numbers

  7. Lesson 7

    Lesson 27: Multiples, Least Common Multiple, Equivalent Division Problems

  8. Lesson 8

    Lesson 28: Two-Step Word Problems, Average, Part 1

  9. Lesson 9

    Lesson 29: Rounding Whole Numbers, Rounding Mixed Numbers, Estimating Answers

  10. Lesson 10

    Lesson 30: Common Denominators, Adding and Subtracting Fractions with Different Denominators

  11. Lesson 11

    Investigation 3: Coordinate Plane