Multiplying and Dividing Decimals

1. Multiplying and Dividing Decimals Section 1-3 (Pages 17-22)

2. Review… Estimate each quotient using compatible numbers. 1. 24.8 ÷ 4.9 2. 103.8 ÷ 13.2 3. 128.62 ÷ 9.86 4. 41.77 ÷ 6.07 About 5 About 8 About 13 About 7

3. Properties of Multiplication Identity Property The product of 1 and “a” is “a”. 5 x 1 = 5 1 x 5 = 5 Zero Property The product of 0 and any number is 0. 5 x 0 = 0 0 x 5 = 0

4. Properties of Multiplication Commutative Property Changing the order of factors does not change the product. 5 x 2 = 2 x 5 Associative Property Changing the grouping of factors does not change the product. (3 x 2) x 5 = 3 x (2 x 5)

5. To multiply decimals… Step 1: Multiply as if the factors are whole numbers. Step 2: Add the number of the decimal places in both factors to find the number of decimal places in the product.

6. Example Find the product of 0.2 x 0.7 Step 1: Multiply as with whole numbers. 2 x 7 14 Step 2: Locate the decimal point. 0.2 x 0.7 0.14 1 decimal place 1 decimal place 2 decimal places

7. Example Find the product of 1.45 x 2.6. Step 1: Multiply as with whole numbers. Step 2: Locate the decimal point.

8. Example Find the product of 1.02 x 3.6. Step 1: Multiply as with whole numbers. Step 2: Locate the decimal point.

9. Multiplying using the Properties… Use mental math to find 2 x 4.097 x 0.5 We know that 2 x 0.5 will give us 1 and then the product of 1 and 4.097 is 4.097. 2 x 4.097 x 0.5 = 2 x 0.5 x 4.097 Commutative Property Associative Property = (2 x 0.5) x 4.097 = 1 x 4.097 Simplify = 4.097 Identity Property

10. Example Use mental math to find the product of 1.09 x 23.6 x 0.

11. Example Use mental math to find the product of 2.5 x 6.3 x 4.

12. Additional Problems 1. 1.45 x 2.6 2. 1.3 x 0.005 3. 41 x 7.5 4. 0 x 2.78 x 1 5. 5 x (4.3 x 1)