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The Ladder Method

The Ladder Method. For Finding LCD, GCF and Simplifying Fractions. Becky Afghani, LBUSD Math Curriculum Office, 2003. The Ladder Method. is a method of factoring which allows you to factor two numbers at once in order to… find the LCM of the two numbers find the GCF of the two numbers

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The Ladder Method

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  1. The Ladder Method For Finding LCD, GCF and Simplifying Fractions Becky Afghani, LBUSD Math Curriculum Office, 2003

  2. The Ladder Method... is a method of factoring which allows you to factor two numbers at once in order to… • find the LCM of the two numbers • find the GCF of the two numbers • simplify a fraction with these numbers as numerator and denominator Becky Afghani, LBUSD Math Curriculum Office, 2003

  3. Use the ladder to factor6 and 8 You will divide out any common factors of the two numbers 2 6 8 3 4 What number goes into both 6 and 8? Now divide both 6 and 8 by the 2 Does any # besides 1 go into both 3 and 4? No? Then you are done. Becky Afghani, LBUSD Math Curriculum Office, 2003

  4. x x Let’s find the Least Common Multiple (LCM) of 6 and 8 The LCM is the product of all the numbers on the left and the bottom. The LCM of 6 and 8 is 24. 2 6 8 3 4 =24 Becky Afghani, LBUSD Math Curriculum Office, 2003

  5. The “L” shape gives you the LCM: multiply the numbers on the left and bottom. Which numbers in the ladder give you the LCM? # # # # # # # # # # # Becky Afghani, LBUSD Math Curriculum Office, 2003

  6. What about the Greatest Common Factor (GCF) of 6 and 8? The GCF is the product of all the numbers on the left. The GCF of 6 and 8 is 2. 2 6 8 3 4 Becky Afghani, LBUSD Math Curriculum Office, 2003

  7. Multiply the numbers on the left only for the GCF. Which numbers in the ladder give you the GCF? # # # # # # # # # # # Becky Afghani, LBUSD Math Curriculum Office, 2003

  8. simplifies to How can we use the Ladder Method to simplify ? The simplified numerator and denominator are on the bottom. 2 6 8 3 4 Becky Afghani, LBUSD Math Curriculum Office, 2003

  9. The numbers on the bottom of the ladder are your simplified numerator and denominator. Which numbers in the ladder give you the simplified fraction? # # # # # # # # # # # Becky Afghani, LBUSD Math Curriculum Office, 2003

  10. Let’s try some bigger numbers. Divide out all the common factors down the left side. 2 24 60 What number goes into both 24 and 60? Does any # besides 1 go into both 12 and 30? 2 12 30 How about 6 and 15? Anything else? 3 6 15 No? You’re done. 2 5 Becky Afghani, LBUSD Math Curriculum Office, 2003

  11. 2 24 60 x 2 12 30 x 3 6 15 x x 2 5 Find the LCM. The LCM of 24 and 60 is 120. = 120 Becky Afghani, LBUSD Math Curriculum Office, 2003

  12. 2 24 60 x 2 12 30 x 3 6 15 2 5 Find the GCF. The GCF of 24 and 60 is 12. = 12 Becky Afghani, LBUSD Math Curriculum Office, 2003

  13. simplifies to . 2 24 60 2 12 30 3 6 15 2 5 Simplify . Becky Afghani, LBUSD Math Curriculum Office, 2003

  14. Simplified fraction = Practice. Find the LCM and GCF for 28 and 42. Simplify . LCM = 2  7  2  3 = 84 2 28 42 GCF = 2  7 = 14 7 14 21 2 3 Becky Afghani, LBUSD Math Curriculum Office, 2003

  15. 2 28 42 7 14 21 2 3 Extension Questions 1. Do you have to factor out prime numbers? 2. Can you factor three numbers at once and still get the right GCF and LCM? Try factoring small numbers to find out - like 4, 6, and 8. Becky Afghani, LBUSD Math Curriculum Office, 2003

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