# GCF AND LCM

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Determining the Lowest Common Multiple (LCM) of whole numbers . 1. The lowest common multiple (LCM) of two or more numbers is the smallest common multiple of these numbers. Find the lowest common multiple of 4 and 6 Solution: Method 1 : List all multiples Multiples of 4 : 4, 8, 12, 16, 20, 24, … Multiples of 6 : 6, 12, 18, 24, … Therefore, the LCM of 4 and 6 is 12. Method 2: Algorithm 2 2 3 1 1 Therefore the LCM of 4 and 6 is 2 x 2 x 3 = 12 4 6 2 3 1 3 Keep dividing by the smallest prime factor until you get 1. Carry down the numbers that are not divisible by the prime factors Multiply all the divisors.

### PowerPoint Presentation:

Find the lowest common multiple of 6, 12 and 20 Solution: 2 2 3 5 1 1 1 Therefore, the lowest common multiple of 6, 12 and 20 is 2 x 2 x 3 x 5 = 60 6 12 20 3 6 10 3 3 5 5 1 1

### PowerPoint Presentation:

Determining the highest common factor (HCF) of whole numbers. 1. Find the highest common factor of 20 and 30 Solution: Method 1 : List all factors Factors of 20 : 1, 2, 4, 5, 10, 20 Factors of 30 : 1, 2, 3, 5, 6, 10, 15, 30 Therefore, the HCF of 20 and 30 is 10 Method 3: Algorithm 2 5 2 3 Therefore the HCF of 20 and 30 is 2 x 5 = 10 20 30 10 15 Stop dividing when there are no more common factors except 1. Multiply all the divisors.