Today we will multiply using decimals.

1. Today we will multiply using decimals. multiply = Multiply means to add all equal groups together a set number of times Decimals=numbers less than zero

2. Multiplying Decimals Remember the 100’s chart? When you multiply two numbers that are decimals, you get the product! Here is a model of the product of0.7and0.3. 0.7 0.3 1 1 Because 21 of the 100 squares are shaded, 0.70.3 = 0.21. APK

3. You go to the store to buy an iPod. The price is $199.00 for an iPod Touch. Do you pay $199.00 or do you pay 217.41? You pay 217.41 because of sales tax and you must multiply by .0925% to calculate the tax.

4. Multiply • Multiply means to add all equal groups together a set number of times • Example: 4 x 3=12 12 =

5. Decimal • A decimal is a number less than 1. For example • $0.70 • 10.50989 • $25.50

6. Importance • When you purchase something in the store, you always need to know how much it will cost with sales tax. • It will help you on any tests! • What would be other reasons to know how to multiply with decimals?

7. Let’s try one together! Multiplying Decimals 1 2 3.2 1 x 4 Ignore the decimal point and just multiply!! 1St step: 4 1 2 8 . Count the number of digits that follow the decimal. 2St step: 2 1 Check by using estimation. Place the decimal. 3rd step: Pg. 1 Pg. 2

8.  + ––– –––––– Let’s try some more! • Ignore the decimal and just multiply • Count the number of digits that follow the decimal • Place the decimal 5.82 2 decimal places 0.41 2 decimal places 582 2328 ––––––– 4 decimal places 2.3862 1 2 3 4

9. 6 0.4 Checking Reasonableness To check that the product in the example is reasonable, round each factor to the place value of the leading digit, then multiply. The leading digit of a number is the first nonzero digit. 5.82 Round to the nearest whole number. 0.41 Round to the nearest tenth. Because 6 0.4 = 2.4, the product of the previous example is reasonable.

10.  + ––– –––––– CHECK After you place the decimal point, you can drop any zeros at the end of an answer. Multiplying Decimals • Ignore the decimal and just multiply • Count the number of digits that follow the decimal • Place the decimal 6.45 2 decimal places 18 0 decimal places 5160 645 –––––– 116.10 2 decimal places ANSWER 6.45  18 = 116.1 Because 6  20 = 120, the product is reasonable.

11.  + ––– ––––––– CHECK 1.273 3 decimal places 0.06 2 decimal places • Ignore the decimal and just multiply • Count the number of digits that follow the decimal • Place the decimal 0.0 7638 5 decimal places ANSWER 1.273  0.06 = 0.07638 Because 1  0.06 = 0.06, the product is reasonable.

12. 9.76 x5.9 9.76 x5.9 9.76 x5.9  –––––– 9.76 5.9 • Ignore the decimal and just multiply • Count the number of digits that follow the decimal • Place the decimal 8 7 8 4 4 8 80 ––––––– 57.584 1 2 3

13.  –––––– 1.92 5.3 • Ignore the decimal and just multiply • Count the number of digits that follow the decimal • Place the decimal 5 7 6 9 6 0 ––––––– 10.176 1 2 3

14. Ignore the decimal and just multiply • Count the number of digits that follow the decimal • Place the decimal

15. Let’s review what we learned! What does multiply mean? multiply = Multiply means to add all equal groups together a set number of times What are decimals? Decimals=numbers less than zero