1. Multiplying Decimals NS3
I can multiply decimals.

2. Multiply Decimals Step 1 --- Ignore the decimal
Step Rewrite the problem
Step Multiply the problem
Step Count the decimal places
Step Move decimal that many places in your answer

3. Guided Practice X

4. Multiplying Decimals
You can use graph paper to model decimal multiplication. Here is a model of the product of 0.7 and 0.3.
0.7
0.3 1
Because 21 of the 100 squares are shaded, 0.7  0.3 = 0.21 1
NOTE
BOOK
Multiplying Decimals
Multiply decimals as you would whole numbers. Then place the decimal point in the product. The number of decimal places in the product is equal to the sum of the number of decimal places in the factors.
Words
Numbers
0.7  0.3 = 0.21

5. Multiplying Decimals 1  5.82 –––––– 0.41 ––– 5 8 2 2 3 2 80 –––––––
EXAMPLE 1
5.82
2 decimal places
–––––– 
0.41
––– +
2 decimal places
5 8 2
–––––––
4 decimal places 4 3 2 1

6. Example: 5.63 x 3.7
5.63 x
3.7

7. Multiplying Decimals 2  6.45 –––––– 18 ––– 5160 6450 –––––– 116.10
EXAMPLE 2
6.45
2 decimal places
––––––  18
0 decimal places
––– +
5160
6450
––––––
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.

8. 2 Multiplying Decimals   Multiplying Decimals 6.45 1.273 –––––– 18
EXAMPLE 2
Multiplying Decimals
6.45
2 decimal places
1.273
3 decimal places
––––––  18
0 decimal places
––– +
––––––– 
0.06
2 decimal places
––– +
5160
0.0
7638
5 decimal places
645
––––––
116.10
2 decimal places
Write a zero before the 7 as a placeholder so that the number has 5 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
ANSWER
1.273  0.06 =
CHECK
CHECK
Because 6  20 = 120, the product is reasonable.
Because 1  = 0.06, the product is reasonable.

9. 3 Multiplying Decimals to Find Area
EXAMPLE 3
Multiplying Decimals to Find Area
Central Park Central Park is a rectangular park about 2.5 miles long and about 0.5 mile wide. What is the area of Central Park?
SOLUTION
A = l w
Write formula for area of a rectangle.
= l w
2.5
(0.5)
Substitute 2.5 for l and 0.5 for w.
= 1.25
Multiply.
ANSWER
The area of Central Park is about 1.25 square miles.

10. Showdown!!!!
3. 2 x .006 =
.012
x 2.52 =
1.6632
x .7 =
.217
x .03 =
.027