Lesson 4.2 Adding and Subtracting Decimals November 7, 2007

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 + 7.81 Line up the decimal + -30.78 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