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The Ladder Method

The Ladder Method. For Finding GCF and LCM. 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 GCF of the two numbers find the LCM of the two numbers.

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The Ladder Method

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  1. The Ladder Method For Finding GCF and LCM 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 GCF of the two numbers • find the LCM of the two numbers 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 making the ladder. Becky Afghani, LBUSD Math Curriculum Office, 2003

  4. What is the Greatest Common Factor (GCF) of 6 and 8? The GCFisthe 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

  5. 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

  6. 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? 12 30 2 How about 6 and 15? Anything else? 6 15 3 No? You’re done. 2 5 Becky Afghani, LBUSD Math Curriculum Office, 2003

  7. 2 24 60 x 12 30 2 x 6 15 3 2 5 Find the GCF. The GCF of 24 and 60 is 12. = 12 Becky Afghani, LBUSD Math Curriculum Office, 2003

  8. 2 24 60 x 12 30 2 x 6 15 3 x x 2 5 Find the LCM. The LCM of 24 and 60 is 120. = 120 Becky Afghani, LBUSD Math Curriculum Office, 2003

  9. Practice. Find the LCM and GCF for 28 and 42. 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

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