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** __Goal of this Lesson__: We will learn how to estimate sums and differences of decimals. Here is a sample problem: 898.8 - 379.26 = ???
 * [[image:http://wyoming5mathwiki.wikispaces.com/file/view/]]Estimating sums and differences

Can you answer that problem? Bet you can't--but at the end of this lesson you should be able to! __**Using Estimations**__: Basically there is no one way to get a correct answer when estimating. We use estimates to get answers more quickly. There are 3 methods that can help us get the answer: **__ Refer to the attached powerpoint presentation for an example of each method :__** **Rounding**: Round each number to the nearest 10 for easy adding. 50.5 + 68.1 = 118.6 actual result; **__OR__** 50 + 70 = 120 as estimated
 * Rounding: you can estimate by rounding each decimal to the nearest whole number that is easy to add or subtract in your head.
 * Front-end Estimation: you can estimate by first adding or subtracting the front digits. Then you add or subtract the next digits.
 * Clustering: you can estimate by rounding a group of close numbers to the same number.

42.6 - 21.2 = 21.4 actual result; __**OR**__ 4-2 = 2 and 2-1= 1 or 21 as estimated
 * Front End Estimation**: add or subtract the front digits, then the next.

22+21+23 = 63 actual result; **__OR__** 20+20+20 = 60 as estimated
 * Clustering**: rounding a group of close numbers to the same number.

Have you figured out the answer to the sample problem yet? Hint : It's easy if you round by tens. answer: 500 as estimated.



Links: You can use these sites to help you learn more about using estimations. http://www.mathleague.com/help/decwholeexp/decwholeexp.htm#estimating http://www.321know.com/est73ax2.htm| http://www.glencoe.com/sec/math/msmath/mac04/course1/study_guide/pdfs/mac1_pssg03.pdf