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Lesson 3.3 Adding and Subtracting Decimals

Lesson 3.3 Adding and Subtracting Decimals. Essential Question:. How do I add and subtract decimals? Always line up decimals Add and subtract like you always do Bring decimal straight down in your answers. Adding. Examples: 4.55 + 11.3.

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Lesson 3.3 Adding and Subtracting Decimals

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  1. Lesson 3.3 Adding and Subtracting Decimals

  2. Essential Question: • How do I add and subtract decimals? • Always line up decimals • Add and subtract like you always do • Bring decimal straight down in your answers

  3. Adding Examples: 4.55 + 11.3 Put the first number on the top of the second number and line up the decimals. You can add a zero to help keep everything lined up When adding or subtracting you always start from the right and work left. 4.55 + 11.3 0 15.85

  4. 6.44 + 16 When there is not a decimal put one behind the number. Line up the decimal Add a zero to line up everything 6.44 + 16. 0 22.44

  5. -8.33 + -10.972 -8.33 -10.972 Line up the decimal Add a zero to line up everything 0 + Same signs Add – keep the sign -19.302

  6. Subtracting Examples: 5.34 -2.08 Put the first number on the top of the second number and line up the decimals. Different signs Take difference 5.34 -2.08 3.26

  7. -38.59 – (-7.81) -38.59 + 7.81 Line up the decimal + -30.78 Subtract to add when negatives are used. Different signs take difference

  8. 28 – 15.911 When there is not a decimal put one behind the number. Add zeros to line up everything, then subtract 7 9 9 28. -15.911 000 . 1 2 0 8 9

  9. Magic Square The sum of each row, column, and diagonal must be the same. Sums to 13.875

  10. Estimation • You can always estimate to know if your answer is close. • 6.7 + 8.2 = • Ask yourself, “Is 6.7 closer to 7 or 6?” • Ask yourself, “Is 8.2 closer to 8 or to 9?” • Your estimate is 7 + 8 = ________ • Actual answer?? _______________ 7 8

  11. Estimate and solve the following…(E = Estimate, A = Actual) 8.9 + 3. 4 E=______ A = _______ 7.4 – 2.1 E= ______ A = _______ 6.7 – 4.3 E= ______ A = _______ 2.9 + 1.8 E= ______ A = _______ Watch the signs!!

  12. Ms. Kim is making 3 different kinds of cookies using chocolate chips. The recipes ask for 2.25 kg, 1.75 kg, and 4.55 kg of chocolate chips. Ms. Kim has 11 kg of chocolate chips total. • Estimate to find out how much Ms. Kim needs. Then find the actual amount. • Does she have enough to make the cookies? • If your answer is “NO”, how much more does Ms. Kim need to make the cookies? If your answer is “YES”, how much does she have leftover?

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