# Multiplying Decimals - PowerPoint PPT Presentation

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Multiplying Decimals. Ms. Mayner. or. Strategy #1. 405 x 59. 405 x 59. 405 x 9. 405 x 50. +. 3. 6. 4. 4. 5. 2. 0. 2. 2. 5. 0. (5 x 4) = 20 Since there are no other numbers to multiply, write down the 20. (5 x 0) + 2 = 2 Write down the 2.

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Multiplying Decimals

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## Multiplying Decimals

Ms. Mayner

or

### Strategy #1

405 x 59

405

x 59

405

x 9

405

x 50

+

3

6

4

4

5

2

0

2

2

5

0

(5 x 4) = 20

Since there are no other numbers to multiply, write down the 20.

(5 x 0) + 2 = 2

Write down the 2.

Zero is a place holder. Put a zero in your answer to hold its place.

(9 x 0) + 4 = 4

Write down the 4.

5 x 9 = 45

Put the 5 in the answer and carry the 4 (it’s really 40) to the next place value (tens)

5 x 5 = 25

Put the 5 in the answer and carry the 2 (it’s really 20) to the next place value (tens)

(9 x 4) = 36

Since there are no other numbers to multiply, write down the 36.

or

405 X 59

405

x 59

405

x 9

405

x 50

+

3

6

4

4

5

2

0

2

2

5

0

23,895

### MULTIPLYING DECIMALS: Things you need to know…

• Do not line up the decimal points!

• Instead, place the number with more digits on top.

• Line up the other number underneath, at the right.

• Pretend all decimals are whole numbers until the very end

• Only look at the decimals when trying to figure out where to put the decimal point in your answer

1

Decimal Places

4

2

5.63

two

x

3.7

one

1

1

39

4

1

1

+

16

8

9

0

2

0

.

8

3

1

three

### Example: 0.53 x 2.618

2.618 has more digits (4) than 0.53 (3), so it goes on top.

3

4

Decimal Places

1

2

2.618

three

x

0.53

two

1

7

8

5

4

13

0

9

0

0

+

0

0

0

0

00

.

1

3

8

7

5

4

five

3

1

2

1

15.3

one

x

6.5

one

1

7

6

5

+

9

1

8

0

.

9

9

4

5

two

### Homework

• Multiplying Decimals Page 47 #1 d-g, 2 a-d, 9

• 2.5 Multiplying Decimals Page 48-49 # 3, 5, 9, 11