 # Today we will multiply using decimals.

## Presentation on theme: "Today we will multiply using decimals."— Presentation transcript:

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 LO

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 of 0.7 and 0.3. 0.7 0.3 1 1 Because 21 of the 100 squares are shaded, 0.7  0.3 = 0.21. APK

You go to the store to buy an iPod. The price is \$199
You go to the store to buy an iPod. The price is \$ for an iPod Touch. Do you pay \$ or do you pay ? You pay because of sales tax and you must multiply by .0925% to calculate the tax. APK

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

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

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? IMP

Multiplying Decimals 1 2 3.2 1 x 4 4 1 2 8 . Let’s try one together!
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

 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 5 8 2 ––––––– 4 decimal places 4 3 2 1

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 6 Round to the nearest whole number. 0.41 0.4 Round to the nearest tenth. Because 6  0.4 = 2.4, the product of the previous example is reasonable.

 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 After you place the decimal point, you can drop any zeros at the end of an answer. ANSWER 6.45  18 = 116.1 CHECK Because 6  20 = 120, the product is reasonable.

 1.273 ––––––– 0.06 ––– Ignore the decimal and just multiply
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 = CHECK Because 1  = 0.06, the product is reasonable.

 9.76 –––––– 5.9 Ignore the decimal and just multiply
9.7 6    x   5.9      9.7 6    x   5.9      9.7 6    x   5.9 9.76 –––––– 5.9 Ignore the decimal and just multiply Count the number of digits that follow the decimal Place the decimal 4 8 80 ––––––– 3 1 2

 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 ––––––– 3 2 1

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

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