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# Factors And Primes

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### Factors And Primes

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