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Lesson 3: Decimals (Group Lesson) Add, Subtract, Multiply & Divide 28.9 + 32.5 61.4 Period 3, 5: 9/17/15 Period 2, 4, 6: 9/18/15 Group Lesson

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Lesson Objective SWBAT … 1)Add numbers with decimals. 2)Subtract numbers with decimals. 3)Multiply numbers with decimals. 4)Divide numbers with decimals.

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Adding or Subtracting Decimals Key Points (review, don’t write down) Write the numbers in a vertical column, aligning digits according to their places. Attach extra zeros to the right end of each number so each number has the same amount of digits. Add or subtract as though the numbers are whole numbers. Place the decimal point in the sum or difference to align with the decimal point in the respective operation.

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Adding Decimals Add the ones. There are 18 ones. Add the tenths 8.784 2.560 +6.721 Add the hundredths. 1 2 0 Add up the thousandths. So 8.784 + 2.56 + 6.721 = 18.065.

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Subtracting Decimals Subtract the thousandths. 4.040 -2.681 1.359 So, 4.040 – 2.681 = 1.359 Subtract the hundredths. There are 5 hundredths. Subtract the tenths. There are 3 tenths. Subtract the ones. There is 1 one. 9 13 10

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Multiply Decimals Key Points (review, don’t write down): Multiply the decimal numbers as though they are whole numbers. Count the digits in the decimal parts of both decimal numbers. Place the decimal point in the product so that there are as many digits in its decimal part as there are digits you counted in the previous step. If necessary, attach zeros to the left end of the product to place the decimal point accurately. 21.4 x 0.36 3 total decimal places 7 704.

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Look at this example. 3.45 x 4.082 = How many places are there to the right of the decimal point? Five; so, the answer will have five places to the right of the decimal. The answer is 14.08290 The last zero can be dropped and the answer would be 14.0829. Examples 920 x 3.7 = 3404.0 0.00079 x 0.025 = 0.00001975 Class Examples 870 x 4.6 = 4002.0 0.000086 x 0.057 = 0.000004902

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Dividing decimals is similar to dividing whole numbers. Same question…what about the decimal place? Where does that go? Steps 1.Make the divisor a whole number by shifting the decimal to the right as many times as necessary. 2.Move the decimal in the dividend the same number of times that we moved it in the divisor 7 0 64 2 0 9..0?????? Division of Decimals

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Dividing decimals…… Steps: 1.Add zeros to the end of the dividend so that we can round to the desired place value – Example: Round quotient to nearest tenth write 2 zeros after the decimal – Round quotient to nearest thousandth need 4 zeros after the decimal 70642090.00 70642090.0000

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Dividing decimals……. Steps 1.Do the division as if it were whole numbers 2.Put the decimal place in the quotient directly over the decimal point in the dividend 70642090.00 00059.61 ≈ 59.6

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Each of the digits are the same. Each of the steps are the same. But the place values are different because of the decimal points. -570 76 -76 0 -57 0 7 6 -7 6 0 Examples # -57 0 7 6 -7 6 0

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Whiteboard CFU Quiz Your Group Evaluate the expression: 43-27.4

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Whiteboard CFU Quiz Your Group 45.56+ 23 + 4.5

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Whiteboard CFU Quiz Your Group 9-0.5+ 4.67

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Whiteboard CFU Quiz Your Group 15.5 X 26.77

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