1. Welcome to this IRSC Adult Education Live Virtual Lesson
Diana Lenartiene, Ed. S. moderator/instructor

2. Introducing… your virtual classroom
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Let me give you a quick tour of our virtual classroom so you may know how to get simple interact with me! Pay attention, there will be a quiz at the end!
6/10/2008; updated: 10/3/11
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6/10/2008; updated: 10/3/11
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6/10/2008; updated: 8/4/2009
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7. Adding and Subtracting Decimals
Solve problems involving addition and subtraction of decimals.

8. We will now watch a video on adding and subtracting
with decimals

9. To add decimals
Line up the decimal points and add the columns from right to left.
Place a decimal point in the answer directly below the other decimal points.

10. Example 1 0.64 + 0.39 Line up the decimal points. 0.64 + 0.39
+ 0.39
__________________________
Add the columns.
1.03

11. Example 2 5.74 + 3.3 Line up the decimal points. 5.74 + 3.3
+ 3.3
_____________________________
Add the columns.
9.04

12. Try this one on your own! 39.66 +22.7 Remember, line up the decimals,
Place the decimal point in the answer under the ones in the problem,
Add like whole numbers.

13. Answer 11
39.66
+22.7
62.36

14. To subtract decimals Line up the decimal points.
Subtract the columns from right to left, regrouping if necessary.
Place a decimal point in the answer directly below the other decimal points.

15. Example 1 0.37 0.86 – 0.49 Line up the decimal points 0.86 - 0.49
__________________________
Regroup the tenths. Subtract the columns. 7 16
0.37

16. We will now watch a video on multiplying with decimals

17. Multiplying Decimals
0.7
You can use graph paper to model decimal multiplication. Here is a model of the product of 0.7 and 0.3.
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

18. 1 Multiplying Decimals  Multiplying Decimals 5.82 –––––– 0.41 –––
EXAMPLE 1
Multiplying Decimals
5.82
2 decimal places
–––––– 
0.41
––– +
2 decimal places
5 8 2
–––––––
4 decimal places 4 3 1 2

19. Multiplying Decimals
Checking Reasonableness To check that the product in Example 1 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.

20. 2 Multiplying Decimals  Multiplying Decimals 6.45 –––––– 18 ––– 5160
EXAMPLE 2
Multiplying Decimals
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.

21. 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.

22. 3 Multiplying Decimals 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.

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Thank you for viewing this presentation.
Diana Lenartiene, IRSC ABE Instructor