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Published byZoe Ball Modified over 7 years ago

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Adding and subtracting decimal numbers Written methods

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Addition Example 2.15 + 1.77 2. 1 5 2. 1 5 + 1. 7 7 + 1. 7 7 1 2. 1 5 2. 1 5 + 1. 7 7 + 1. 7 7 2 1 2. 1 5 2. 1 5 + 1. 7 7 + 1. 7 7 3. 9 2 3. 9 2 5+7=12 so write the 2 underneath and carry 1 over to the tens column (this may also be written under the answer) 7+1+1=9 so write the 9 underneath then repeat the process for the hundreds column. When adding/subtracting decimals remember to line up the decimal points

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Subtraction Example 22.5 – 1.77 2 2. 5 0 2 2. 5 0 - 1. 7 7 - 1. 7 7 4 1 4 1 2 2. 5 0 2 2. 5 0 - 1. 7 7 - 1. 7 7 3 3 1 14 1 1 14 1 2 2. 5 0 2 2. 5 0 - 1. 7 7 - 1. 7 7. 7 3. 7 3 1 14 1 2 2. 5 0 1 14 1 2 2. 5 0 - 1. 7 7 - 1. 7 7 2 0. 7 3 2 0. 7 3 4 - 7= a negative number so borrow one from the units column. Now we have 14 – 7 = 7. Make sure that both numbers have the same amount of digits after the decimal point by adding a zero. 0 – 7 = a negative number so borrow one from the tenths column. Now we have 10 – 7 = 3. Now complete the sum, 1 – 1 = 0, 2 – 0 = 2.

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