Chapter 5Add and Subtract Decimals

Lesson 1 – Round Decimals

1. Underline the digit in the place to which you want to round.

2. Look at the digit to the right and use the rules for rounding. (0,1,2,3,4 → keep the digit; 5,6,7,8,9 → go up to the next digit)

3. Either drop the remaining digits or change them to zeros.

Example: Round 5.476 to the hundredths place.

5.476 → 5.48 or 5.480

Lesson 2 – Estimate Sums and Differences

•Round to either the ones place or the tens place.

Example: Estimate 42.3 + 57.9

42.3 → 42 or 42.3 → 40 + 57.9 →+58 + 57.9 →+60

100 100

Lessons 6 & 10 – Adding and Subtracting Decimals

1. Write the problem vertically. Make sure you line up the decimals.

2. You can add zeros to any blank spaces.3. Add or subtract.

Example: Find 75.93 – 52.7

75.93 - 52.70

23.23

Lesson 7 – Addition Properties

•Commutative Property of Addition ▫The order in which the numbers are added

does not change the sum.▫Ex. – 5 + 4 = 4 + 5

•Associative Property of Addition▫The way in which the numbers are grouped

does not change the sum.▫Ex. – (7 + 3) + 9 = 7 + (3 + 9)

• Identity Property of Addition▫The sum of any number and 0 equals the

number.▫Ex. - 12 + 0 = 12