Today we will multiply using decimals

Today we will multiply using decimals.

multiply = Multiply means to add all equal groups together a set number of

timesDecimals=numbers less than zero

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 0.3.1

1

0.3

0.7

Because 21 of the 100 squares are shaded, 0.7 0.3

Multiplying Decimals

= 0.21.

APK

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.

Multiply

• Multiply means to add all equal groups together a set number of times

• Example: 4 x 3=12

= 12

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?

3.2 1x 4

4 8 1 2 .

1St step:Ignore

the decimal

point and

just multiply!!

2St step:Count the

number

of digits

that follow

the decimal.

12

12

Pg. 1 Pg. 23rd step:Place the

decimal.

Check by

using estimation.

Let’s try one together!

5.82

0.41

2 decimal places

2 decimal places

5 8 22 3 2 8

4 decimal places

–––+––––––

2.3 8 6 2–––––––

1234

Let’s try some more!

1. Ignore the decimal and just multiply

2. Count the number of digits that follow the decimal

3. Place the decimal

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

0.41 0.4

Round to the nearest whole number.

Round to the nearest tenth.

Because 6 0.4 = 2.4, the product of the previous example is reasonable.

6.45

18

2 decimal places

0 decimal places

5160645

––––––116.10

Because 6 20 = 120, the product is reasonable.

Multiplying Decimals

–––+––––––

After you place the decimal point, you can drop any zeros at the end of an answer.

2 decimal places

CHECK

ANSWER 6.45 18 = 116.1

1. Ignore the decimal and just multiply

2. Count the number of digits that follow the decimal

3. Place the decimal

1.273

0.06

3 decimal places

2 decimal places

76380.0 5 decimal places

Because 1 0.06 = 0.06, the product is reasonable.

––––––– –––+

CHECK

ANSWER 1.273 0.06 = 0.07638

1. Ignore the decimal and just multiply

2. Count the number of digits that follow the decimal

3. Place the decimal

1. Ignore the decimal and just multiply

2. Count the number of digits that follow the decimal

3. Place the decimal

9.7 6   x   5.9

9.7 6   x   5.9

9.7 6   x   5.9

9.76

5.9

8 7 8 44 8 80

––––––

57. 5 8 4–––––––

123

1. Ignore the decimal and just multiply

2. Count the number of digits that follow the decimal

3. Place the decimal

1.92

5.3

5 7 69 6 0

––––––

10. 1 7 6–––––––

123

1. Ignore the decimal and just multiply

2. Count the number of digits that follow the decimal

3. Place the decimal

Let’s review what we learned!

multiply = Multiply means to add all equal groups

together a set number of times

What does multiply mean?

What are decimals?

Decimals=numbers less than zero