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# Factors And Primes

## on Feb 02, 2009

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## Factors And PrimesPresentation Transcript

• Multiples,Factors and Primes
• Objectives
• In this lesson you will get to work on
• finding lowest common multiples
• finding Factors of numbers
• finding highest Common Factors
• finding Prime numbers
• Lowest Common Multiple
• The lowest common multiple(LCM) of 3 and 4 is the lowest number which is in both the 3 and 4 times table.
• First list out the 3 times tables:
• 3, 6, 9, 12 ,15, ….
• Then list out the 4 times table:
• 4, 8, 12, 16, 20, 24….
• The first number which comes up in both is 12.
• 12 is the most common multiple of 3 and 4.
• Questions
• Find the LCM of these number pairs
• 9 and 6
• 8 and 12
• 9 and 15
• 24 and 18
• The LCM can help us compare fractions.
• Example which is bigger 1 / 6 or 3 / 8 ?
• They are difficult to compare because they have different denominators(the bottom numbers)
• 1 / 6 3 / 8
• Find equivalent fractions which have a common denominator. (same bottom number)
• To find the common denominator find the LCM of 6 and 8 Multiples of 8 are 8, 16, 24, 32.. Multiples of 6 are 6, 12,18, 24.. The LCM of 6 and 8 is 24 Now convert each fraction into 24ths 1 / 6 x 4 = 4 / 24 3 / 8 x 3 = 9 / 24 By finding a common denominator we can can now compare the fractions and see that 3/8 is bigger
• What is a factor?
• A number which divides exactly into another number is called a factor of that number.
• Here is a way to find the factors of 20
• Can 20 be divided by 1 exactly
• 20 ÷ 1 = 20 20 ÷ 5 = 4
• 20 ÷ 20 = 1 20 ÷ 4 = 5
• 20 ÷ 2 = 10
• 20 ÷ 10 = 2 We already have 5 as a factor. This
• 20 ÷ 3 = No means we have listed all the factors of.
• 20 ÷ 4 = 5 20. 1, 2, 4, 5, 10, 20
• Defination
• A number which divides exactly unto another number with no remainders is called a factor of that number.
• List the factors of
• 16
• 1, 2, 4, 8, 16
• 36
• 1, 2, 3, 4, 6, 9, 12, 18, 36.
• 100
• 1, 2, 4, 5, 10, 20, 25, 50, 100
• Highest Common Factors
• What is the biggest number that 18 and 30 can be divided into without leaving a remainder
• List the factors of 18
• 1, 2, 3, 6, 9, 18
• List the factors of 30. 1, 2, 3, 5, 6, 10, 15, 30
• The biggest number in both lists is 6.
• We say that the highest common factor of 18 and 30 is 6.
• Questions
• Find the highest common factors of
• 6 and 15
• 15 and 50
• 12 and 66
• 39 and 52
• 21 and 36 and 60
• Prime numbers
• A prime number is a number that can only be divided by itself and the number 1.
• Write down the prime numbers up to 20
• 2, 3, 5, 7, 11, 13, 17, 19
• Prime Factors
• Can you list the prime factors of the following numbers. In other words list the factors and circle the ones which are prime numbers
• 48
• 1, 2, 3, 4, 6, 8, 12, 16, 24, 28
• 25
• 1, 5, 25
• 17
• 1, 17