 # Adding and Subtracting Fractions Year 6/7 2016. Adding Fractions with Common Denominators.

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Adding and Subtracting Fractions Year 6/7 2016

Let’s Practice!

It’s the same for subtracting!

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

Finding the Lowest Common Denominator The lowest common multiple of two numbers is the lowest number in BOTH lists of multiples The number they can both be divided into Multiples of 2 are 2, 4, 6, 8, 10…… Multiples of 3 are 3, 6, 9, 12, ……… What is the lowest common multiple?

+ The Lowest Common Multiple of 2 and 3 is 6 so turn all fractions into sixths. How will we get there? You can’t add fractions with different denominators 1_31_3 1_21_2 Therefore ?_6?_6 ?_6?_6 ?_6?_6 =+ X X X X

The Lowest Common Multiple of 3 and 7 is ??? so turn all fractions into ???. How will we get there? 4 __ 3 2 __ 7 + = ? __ ? __ ? + = Therefore 4 __ 3 2 __ 7 X X X X

Subtracting Fractions with Different Denominators It’s the same as adding! Find the lowest common multiple.

Subtracting Fractions with Different Denominators

Adding Mixed Numbers Separate the fraction and the whole number sections, add them separately and recombine at the end.