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# 5 Minute Check - PowerPoint PPT Presentation

5 Minute Check. Complete in your notebook. Estimate each product. 1. 9.7 x 3 2. 3.4 x 5 3. 17.5 x 8 Multiply. 4. 1.5 x 6 5. 3.1 x 13 6. 3.48 x 25. 5 Minute Check. Complete in your notebook. Estimate each product. 1. 9.7 x 3. 5 Minute Check.

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Presentation Transcript

Estimate each product.

1. 9.7 x 3

2. 3.4 x 5

3. 17.5 x 8

Multiply.

4. 1.5 x 6

5. 3.1 x 13

6. 3.48 x 25

Estimate each product.

1. 9.7 x 3

Estimate each product.

1. 9.7 x 3

10 x 3 = 30

Estimate each product.

2. 3.4 x 5

Estimate each product.

2. 3.4 x 5

3 x 5 = 15

Estimate each product.

3. 17.5 x 8

Estimate each product.

3. 17.5 x 8

18 x 8 = 144

Multiply.

4. 1.5 x 6

Multiply.

4. 1.5 x 6

1.5 1 decimal place

x 6

9.01 decimal place

Multiply.

5. 3.1 x 13

Multiply.

5. 3.1 x 13

3.1 1 decimal place

x 1 3 Don’t forget the zero

93

+ 310

40.31 decimal place

Multiply.

6. 3.48 x 25

Multiply.

6. 3.48 x 25

3.48 2 decimal places

x 25 Don’t forget the zero

1740

+ 6960

87.002 decimal places

Lesson 3.2 and 3.4

Multiplying Decimals by Decimals

Objective: To understand how to estimate and multiply decimals by decimals.

At the end of this lesson you should be able to answer the following questions.

How do you determine which place value to use when multiplying decimals by decimals?

Why is estimating not as helpful when multiplying very small numbers?

To multiply decimals, multiply as normal and then place the decimal point.

Find the product of 8.7 and 2.8.

First round the numbers to the nearest whole number to get an estimate.

What does 8.7 round to?

Digits from 0 to 4 round down and digits from 5-9 round up.

Find the product of 8.7 and 2.8.

First round the numbers to the nearest whole number to get an estimate.

What does 8.7 round to? 9

What does 2.8 round to?

Find the product of 8.7 and 2.8.

First round the numbers to the nearest whole number to get an estimate.

What does 8.7 round to? 9

What does 2.8 round to? 3

Find the product of 8.7 and 2.8.

First round the numbers to the nearest whole number to get an estimate.

9 x 3 = 27, so

8.7 x 2.8 ≈ 27

Find the product of 8.7 and 2.8.

To multiply decimals.

Step 1 – Stack the numbers with the number with the most digits on top.

8.7

x 2.8

(Since both numbers have 2 digits, either could be on top)

Find the product of 8.7 and 2.8.

To multiply decimals.

Step 2 – Multiply the digits.

8.7

x 2.8

696 Don’t forget to add the zero.

+1740

2436

Find the product of 8.7 and 2.8.

To multiply decimals.

Step 3 – Determine the number of decimal places in the factors to locate the decimal place in the product.

8.7 1 decimal place

x 2.8+ 1 decimal place

696

+1740

24.36 2 decimal places

Find the product of 8.7 and 2.8.

8.7

x 2.8

696

+1740

24.36

Find the product of 8.7 and 2.8.

24.35 ≈ 27

Find the product of .98 and 7.3

Estimate?

Find the product of .98 and 7.3

Estimate?

1 x 7 = 7, so

.98 x 7.3 ≈ 7

Next?

Find the product of .98 and 7.3

.98

x 7.3

Next?

Find the product of .98 and 7.3

.98

x 7.3

294 Don’t forget to add a zero

+6860

7154

Next?

Find the product of .98 and 7.3

.98 2 decimal places

x 7.3+1 decimal place

294

+6860

7.154 3 decimal places

Find the product of .98 and 7.3

.98 2 decimal places

x 7.3+1 decimal place

294

+6860

7.154 3 decimal places

7.154 ≈ 7

Find the product of 3.6 and 0.05.

Estimate?

Find the product of 3.6 and 0.05.

4 x 0 = 0, so

3.6 x 0.05 ≈ 0

Find the product of 3.6 and 0.05.

4 x 0 = 4, so

3.6 x 0.05 ≈ 0

Actual product?

Find the product of 3.6 and 0.05

0.05 2 decimal places

x 3.6+1 decimal place

0030

+ 0015

0.045 3 decimal places

Find the product of 3.6 and 0.05

0.05 2 decimal places

x 3.6+1 decimal place

030

+0150

0.180 3 decimal places

0.180 ≈ 0

Find the product of 0.112 and 7.2

Estimate?

Find the product of 0.112 and 7.2

Estimate?

0 x 7 = 0, so

0.112 x 7.2 ≈ 0

Actual product?

Find the product of 0.112 and 7.2

0.112 3 decimal places

x 7.2+1 decimal place

0224

+07840

.8064 4 decimal places

Find the product of 0.112 and 7.2

0.112 3 decimal places

x 7.2+1 decimal place

0224

+07840

.8064 4 decimal places

0.8064 ≈ 0

Find the product of 1.4 and 0.067

Estimate?

Find the product of 1.4 and 0.067

Estimate?

1 x 0 = 0

1.4 x 0.067 ≈ 0

Actual product?

Find the product of 1.4 and 0.067

0.067 3 decimal places

x 1.4+1 decimal place

0268

+00670

0.0938 4 decimal places

Find the product of 1.4 and 0.067

0.067 3 decimal places

x 1.4+1 decimal place

0268

+00670

0.0938 4 decimal places

0.0938 ≈ 0

Mr. Avery’s car can travel 28.45 miles on one gallon of gas. If his gas tank holds 11.5 gallons, how far can he travel on one tank?

Estimate?

Mr. Avery’s car can travel 28.45 miles on one gallon of gas. If his gas tank holds 11.5 gallons, how far can he travel on one tank?

Estimate?

28 x 12 = 336

Keep in mind

28 x 12 = 28 x 10 + 28 x 2

= 280 + 56 = 336

Actual product?

Mr. Avery’s car can travel 28.45 miles on one gallon of gas. If his gas tank holds 11.5 gallons, how far can he travel on one tank?

28.45 2 decimal places

x 11.5+1 decimal place

14225

28450

+284500

327.175 3 decimal places

Mr. Avery’s car can travel 28.45 miles on one gallon of gas. If his gas tank holds 11.5 gallons, how far can he travel on one tank?

28.45 2 decimal places

x 11.5+1 decimal place

14225

28450

+284500

327.175 3 decimal places

Is this a reasonable answer? 327.175 ≈ 336

Determine whether the following statement is always, sometimes or never true.

The product of two decimals less than 1 is less than either of the factors.

Determine whether the following statement is always, sometimes or never true.

The product of two decimals less than 1 is less than either of the factors.

Always.

0.3 x 0.5 = .15, which is less than 0.3 and 0.5

0.75 x 0.6 = 0.45

Complete the Mid-Chapter Check on page 214. When complete bring to the desk and show Mr. Avery.

Agenda Notes

Homework –Homework Practice 3-2/3-4

Due Thursday, Oct 10

Mid-Chapter 3 Quiz –Thursday, Oct 10