Ch. 1-2 Adding and Subtracting Decimals

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Ch. 1-2 Adding and Subtracting Decimals. August 26, 2013. Example 1 – Aligning decimal points. When adding decimals we will vertically align the decimal points. We will add zeros so each number has the same number of decimal places. Find the sum of 2.31 + 19.1 + 1.882.
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Ch. 1-2 Adding and Subtracting Decimals August 26, 2013 Example 1 – Aligning decimal points
  • When adding decimals we will vertically align the decimal points.
  • We will add zeros so each number has the same number of decimal places.
  • Find the sum of 2.31 + 19.1 + 1.882.
  • How would we align the decimals to add 9.75 + 14.851 + 2?
  • Example 2 - Subtracting Decimals
  • Ipod Shuffle
  • I’m trying to make a playlist on my ipod shuffle and according to my itunes I have 8.34 minutes of space left available. I plan on adding the song, “Cruise” by Florida Georgia Line that is 3.5 minutes long. How many minutes of space will I have left?
  • Will I be able to add another song that is 4.75 minutes long? Why or why not?
  • Example with a partner
  • With the person sitting next to you, set up and and find the following difference.
  • Find 36.901 – 27.824.
  • Show your work and when you arrive at an answer, raise your hand and I’ll come by to check it.
  • Important concepts!!
  • Identity Property of Addition -
  • The sum of Zero and a is a.
  • Algebra : 0 + a = a and a + 0 = a
  • Commutative Property of Addition –
  • Changing the order of the addends does not change the sum.
  • Algebra: a + b = b + a
  • Associative Property of Addition –
  • Changing the groupoing of the addends does not change the sum.
  • Algebra: (a + b) + c = a + (b + c)
  • why do we use these properties?
  • We use these properties of addition to help us to math mentally. If we change the order of numbers using commutative property we can often make compatible numbers.
  • Using the associative property, we can group together numbers add in the order we choose to make it easier to compute.
  • We will use these properties when we do algebra and solve equations.
  • Quick Example:
  • Find 0.7 + 12.5 + 1.3.
  • Homework
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