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Decimals Review

Decimals Review. by Lauren McCluskey. Decimal Models. Tenth. Hundredth. by Christine Berg. Remember that each period has three place values within the period. Ten -thousandths Hundred-thousandths. Tenths Hundredths Thousandths. Hundreds Tens Million Ones. Hundreds

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Decimals Review

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  1. Decimals Review by Lauren McCluskey

  2. Decimal Models Tenth Hundredth by Christine Berg

  3. Remember that each period hasthree place values within the period Ten -thousandths Hundred-thousandths Tenths Hundredths Thousandths Hundreds Tens Million Ones Hundreds Tens Thousand Ones Hundreds Tens Ones Ones 671,690,492.36754 by Moncia Yuskaitis

  4. Equivalent Decimals 0.6 or 6 tenths 0.60 or 60 hundredths by Christine Berg

  5. Use rounding • When the question asks you • to estimate. • When you want to know if your answer is reasonable. by Monica Yuskaitis

  6. Memorize this Poem Find your number. Look right next door. 4 or less just ignore. 5 or more, add 1 more. by Monica Yuskaitis

  7. Round to the tenths: • 75.86 • 75.83 • 75.96 • 75.835

  8. Find your number.Look right next door.4 or less just ignore.5 or more, add 1 more

  9. Find your number.Look right next door.4 or less just ignore.5 or more, add 1 more. • 75.86 is about 75.9 • 75.83 is about 75.8 • 75.96 is about 76.0 • 75.835 is about 75.8

  10. Which is greater: 0.6 or 0.58? 0.6 0.58 by Christine Berg

  11. Which is greater: 0.400 or 0.5? 0.400 0.5 by Christine Berg

  12. Adding or Subtracting Decimals • When adding or subtracting decimals, line them up! What is: • $7.54 + $3.56? • $15.00 - $6.27? • $0.75 + $1.25 + $6.79? • 75.425 + 3.5005? • 98.322 – 7.0545?

  13. Adding Decimals • $7.54 + $3.56? 7.54 + 3.56 11.10 or $11.10

  14. Adding or Subtracting Decimals • When adding or subtracting decimals, line them up! What is: • $7.54 + $3.56 = $11.10 • $15.00 - $6.27 = $8.73 • $0.75 + $1.25 + $6.79 = $8.79 • 75.425 + 3.5005 =78.9255 • 98.322 – 7.0545 = 91.2675

  15. Multiplying Decimals: Step 1: Multiply as if the factors were whole numbers • Multiplying Decimals &Properties of Multiplication by Christine Berg

  16. Step 1: 8.5 X2.5 4 2 5 1 7 0 0 2 1 2 5 next….. • Multiplying Decimals &Properties of Multiplication by Christine Berg

  17. Step 2: Count the total decimals places in the factors • Multiplying Decimals &Properties of Multiplication by Christine Berg

  18. Step 2: 8.5 X2.5 4 2 5 1 7 0 0 2 1 2 5 next….. • Multiplying Decimals &Properties of Multiplication by Christine Berg

  19. Step 3: Give the product the total decimal places of the factors • Multiplying Decimals &Properties of Multiplication by Christine Berg

  20. Step 3: 8.5 X2.5 4 2 5 1 7 0 0 2 1 .2 5 • Multiplying Decimals &Properties of Multiplication by Christine Berg

  21. Multiplying Decimals Why do we count the decimal places? • Multiplying decimals is counter-intuitive. What is 0.10 * 6? • Think about money. 0.10 is a dime, and you have 6 of them, so how much do you have? 0.60.

  22. Multiplying Decimals Or think of base ten blocks where the flat equals one hundred and each rod equals ten…

  23. Multiplying Decimals 0.6 = 0.1 * Or one tenth of 6 tenths is…

  24. Multiplying Decimals 0.06 0.6 = 0.1 * Or… one tenth of 6 tenths is 6 hundredths.

  25. Try it! • 2.50 * 0.1 ? • 87.655 * 0.001? • 125.75 * 1.0?

  26. Try it! • 2.50 * 0.1 = 0.250 • 87.655 * 0.001 = 0.087655 • 125.75 * 0.10 = 12.575

  27. Dividing Decimals When you divide decimals, you move the decimal in the divisor so that it’s a whole number. Then move the decimal in the dividend the same number of places.

  28. How does this work? 10.00 divided by 0.10 0.10 )10.00 becomes: 10 ) 1000 after you move the decimal two places in the divisor and two places in the dividend.

  29. 10 goes into 1000 100 times so the answer is 100. Check it: 100 * .10 = 10.0 or 10.00. It works.

  30. Dividing Decimals • Why does this work? • Dividing decimals can be counter-intuitive. • Dividing a decimal by a decimal can give you a larger number. Now that’s odd, isn’t it? Why is this?

  31. Dividing Decimals Ask yourself: How many ___’s are in ___? 6 tenths 0.6 ÷ 0.1= Or… there are 6 tenths in 0.6.

  32. Try it! • 875.25 ÷ 0.01 ? • 9218.4 ÷ 0.1? • 722.36 ÷ 0.0001?

  33. Try it! • 875.25 ÷ 0.01 = 87,525 • 9218.4 ÷ 0.1 = 92,184 • 722.36 ÷ 0.0001 = 7,223,600

  34. Credits: • Comparing and Rounding Decimals byChristine Berg • Multiplying Decimals &Properties of Multiplication by Christine Berg • Math Flash Place Value by Monica Yuskaitis • Math Flash Rounding by Monica Yuskaitis

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