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1-2 Adding and Subtracting Decimals Do Now: 1.Vocabulary Review: What is place value? Write the value of the digit 8 in each number. 2. 0.385 3. 1.879 4. 812.4 5. 0.23

1-2 Adding and Subtracting Decimals

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1-2 Adding and Subtracting Decimals. Do Now: Vocabulary Review: What is place value? Write the value of the digit 8 in each number. 2. 0.385 3. 1.879 4. 812.4 5. 0.23. Homework Answers 1-1. $6.50 $3.00 $19.50 $4.50 11 5 9 6 12 10. 13 11. 3 12. 10 13. 5 - PowerPoint PPT Presentation

Text of 1-2 Adding and Subtracting Decimals

  • 1-2 Adding and Subtracting DecimalsDo Now: Vocabulary Review: What is place value?Write the value of the digit 8 in each number.2. 0.3853. 1.8794. 812.45. 0.23

  • Homework Answers 1-1

  • Guided Problem Solving 1-11. eight postcards; $.59 each; $2 total2. Estimate the total cost of eight postcards and stamps.3. The product of 8 and $.594. $.605. $4.806. $27. $4.80 1 $2 5 $6.808. yes, 8 3 0.59 1 2 5 6.72, which is close to 6.809. about $4.80

  • Addition PropertiesCommutative Property of Addition: Numbers can be added in any order.Example: 5+3=3+5Associative Property of Addition: Numbers can be grouped in any way.Example: (7+3) + 5 = 7 + (3+5)Identity Property of Addition: The sum of any number and zero is that number.Example: 18 + 0 = 18

  • The Basic Steps:Line up the numbers by the decimal point.Fill in missing places with zeroes.Add or subtract.

  • Mental MathAddition properties can be used to quickly find sums.Example: What is 52 + 12.4 + 48?We can use an addition property to quickly add this. First, change the order: 52 + 48 + 12.4 ________________ property.Then, group the first two addends together: (52 + 48) + 12.4 ________________ property100 + 12.4 = 112.4commutativeassociative

  • Why Estimate?Before adding your numbers, use one of the estimating strategies you learned to see what the answer should be close to.When you add, you can see if your answer is reasonable.

  • Example: 28.9 + 13.31This can estimate to 29 + 13, which is 42. (Rounding)28.913.31+042.21The answer is close to the estimate.

  • SubtractingThe addition properties do not work for subtraction.Estimate and subtract to find what the answer is close to.Subtract to find the real answer.

  • Subtracting Across ZeroesIf you have several zeroes in a row, and you need to borrow, go to the first digit that is not zero, and borrow.All middle zeroes become 9s.The final zero becomes 10.

  • Example: 15 9.372159.372-.0004 9 9 10826.015

  • A marching band has 6.5 minutes to perform at a football game. Does the band have enough time to play America the Beautiful and Yankee Doodle Dandy?

    How long will the band take to play Stars and Stripes Forever and The Star Spangled Banner?

    Title of Band SelectionsMin76 Trombones3.12Stars and Stripes Forever3.52Born in the U.S.A.4.65America the Beautiful3.63Yankee Doodle Dandy2.5The Star-Spangled Banner4.5

  • A marching band has 6.5 minutes to perform at a football game. Does the band have enough time to play America the Beautiful and Yankee Doodle Dandy? The band will play for 6.13 minutes. The band will have enough time.

    2. How long will the band take to play Stars and Stripes Forever and The Star Spangled Banner?8.02 min

    Title of Band SelectionsMin76 Trombones3.12Stars and Stripes Forever3.52Born in the U.S.A.4.65America the Beautiful3.63Yankee Doodle Dandy2.5The Star-Spangled Banner4.5