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

Introducing… your virtual classroom Read 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 Elluminate Meeting/Classroom

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Elluminate Meeting/Classroom Read Let’s try it now… 6/10/2008; updated: 10/3/11 Elluminate Meeting/Classroom

Elluminate Meeting/Classroom Read 6/10/2008; updated: 8/4/2009 Elluminate Meeting/Classroom

Elluminate Meeting/Classroom Read 6/10/2008; updated: 8/4/2009 Elluminate Meeting/Classroom

Adding and Subtracting Decimals Solve problems involving addition and subtraction of decimals.

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

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.

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

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

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.

Answer 11 39.66 +22.7 62.36

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.

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

We will now watch a video on multiplying with decimals

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

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 2 3 2 8 ––––––– 2.3 8 6 2 4 decimal places 4 3 1 2

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.

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.

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 = 0.07638 CHECK CHECK Because 6  20 = 120, the product is reasonable. Because 1  0.06 = 0.06, the product is reasonable.

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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If you still have questions, please contact me at: dlenarti@irsc.edu Thank you for viewing this presentation. Diana Lenartiene, IRSC ABE Instructor