There are two ways to estimate sums and differences when dealing with decimals.

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1. Write each decimal to the nearest whole number. 

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Example: 1.234 + 3.456             =              1 + 3 = 4      

                 3.456 - 1.234              =              3 - 1 = 2

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2. Write only 1 decimal to the nearest whole number. 

1 + 3.456 = 4.456

3.456 - 1 = 2.456