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• 1. 3 8 Adding and Subtracting Fractions By Graeme Henchel http://hench-maths.wikispaces.com
• 2. Adding Fractions with common denominators 3 4 7 + = 8 8 8
• 3. Adding Fractions with different denominators Problem: You can’t add fractions with different denominators without getting them ready first. They will be ready to add when they have common denominators Solution: Turn fractions into equivalent fractions with a common denominator that is find the Lowest Common Multiple (LCM) of the two denominators
• 4. Finding the Lowest Common Denominator • The lowest common multiple of two numbers is the lowest number in BOTH lists of multiples 1 1 + 2 3 Multiples of 2 are 2, 4, 6, 8, 10…… Multiples of 3 are 3, 6, 9, 12, ……… What is the lowest common multiple?
• 5. Finding the Lowest Common Denominator • The lowest common multiple of two numbers is the lowest number they will BOTH divide into 1 1 + 2 3 2 divides into 2, 4, 6, 8….. 3 divides into 3, 6, 9…. What is the lowest number 2 and 3 both divide into?
• 6. 1 1 + 2 3 You can’t add fractions with different denominators + The Lowest Common Multiple of 2 and 3 is 6 so turn all fractions into sixths 1 3 1 2 3 2 5 × + × = + = 2 3 3 2 6 6 6 Special form of 1
• 7. 1 2 + 2 5 Lowest common denominator is 10 so make all fractions tenths 5 4 9 + = 10 10 10
• 8. 1 1 + 3 4 Turn both fractions into twelfths 4 3 7 + = 12 12 12
• 9. ? ? 3 3 2 7 2 9 14 23 × + × = + = + = =1 3 7 3 7 21 21 21 21 21 21 It is 3/3 It is 7/7 So I multiply So I multiply 3/7 by 3/3 2/3 by 7/7 Finally the fractions are READY to add. I just have to add the numerators What is special form 9+14=23 What special form What the lowest number ofBOTH change 7 3 into? 1 of 1 will change will 3 and 7 divide to 21. 21. Hmmmm? to Hmmmm? It is 21. So that is my Hmmmmm?????? common denominator Now 3x3=9 and 2x7=14 Now I know the new numerators
• 10. Adding Mixed Numbers • Separate the fraction and the whole number sections, add them separately and recombine at the end 1 1 2 2 2 +5 2 +5 1 1 3 3 + = = 7+ = 5 6 7 + 5 6 +