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

You can add a zero to help keep everything lined up 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 15.85

Add a zero to line up everything 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. 22.44

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

Subtracting Examples: 5.34 -2.08 5.34 -2.08 3.26 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

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

Add zeros to line up everything, then subtract 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 8 9

The sum of each row, column, and diagonal must be the same. Magic Square 0.5 7 4.625 8.75 The sum of each row, column, and diagonal must be the same. 6.375 0.5 7 5.25 4.625 4 2.25 8.75 2.875 Sums to 13.875

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

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!!

Ms. Kim is making 3 different kinds of cookies using chocolate chips 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?