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Multiplying Decimals Course 1: Lessons and Examples

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Learn to multiply decimals by whole numbers and decimals with helpful hints and examples. Discover how to estimate, evaluate expressions, and solve problems involving decimal multiplication. From warm-ups to real-world applications.

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Multiplying Decimals Course 1: Lessons and Examples

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  1. 3-5 Multiplying Decimals Course 1 L-2 Warm Up Problem of the Day Lesson Presentation

  2. 3-5 Multiplying Decimals Course 1 Warm Up Multiply. 1.87  320 27,840 2. 943  800 754,400 3. 3,806  10 38,060 4. 1,207  100 120,700 5. 72  196 14,112 6. 120  523 62,760

  3. 3-5 Multiplying Decimals Course 1 Problem of the Day Carmen and Rita sold homemade oatmeal cookies. After 8 days, they had sales totaling $70. Each day, their sales were $0.50 higher than the previous day. What were their sales on the first day? $7.00

  4. 3-5 Multiplying Decimals Course 1 Learn to multiply decimals by whole numbers and by decimals.

  5. 3-5 Multiplying Decimals Course 1 Additional Example 1: Science Application Something that weighs 1 lb on Earth weighs 0.17 lb on the Moon. How much would a 4 lb dumbbell weigh on the Moon? Multiply 4 by 0.17, since 1 pound on Earth is 0.17 pound on the Moon. 4  0.17 17 Multiply as you would with whole numbers.  4 68

  6. 3-5 Multiplying Decimals Course 1 Additional Example 1 Continued Something that weighs 1 lb on Earth weighs 0.17 lb on the Moon. How much would a 4 lb dumbbell weigh on the Moon? Place the decimal point by adding the number of decimal places in the numbers multiplied. 0.17 2 decimal places  4 + 0 decimal places 0.68 2 decimal places A 4 lb dumbbell on Earth weighs 0.68 lb on the Moon.

  7. 3-5 Multiplying Decimals Course 1 Check It Out: Example 1 Something that weighs 1 lb on Earth weighs 0.17 lb on the Moon. How much would a 7 lb dumbbell weigh on the Moon? Multiply 7 by 0.17, since 1 pound on Earth is 0.17 pound on the Moon. 7  0.17 17 Multiply as you would with whole numbers.  7 119

  8. 3-5 Multiplying Decimals Course 1 Check It Out: Example 1 Continued Something that weighs 1 lb on Earth weighs 0.17 lb on the Moon. How much would a 7 lb dumbbell weigh on the Moon? Place the decimal point by adding the number of decimal places in the numbers multiplied. 0.17 2 decimal places  7 + 0 decimal places 1.19 2 decimal places A 7 lb dumbbell on Earth weighs 1.19 lb on the Moon.

  9. 3-5 Multiplying Decimals Helpful Hint You can use a decimal grid to model multiplication of decimals. Course 1

  10. 3-5 Multiplying Decimals Multiply. Then place the decimal point. 1 decimal place + 1 decimal place 2 decimal places Course 1 Additional Example 2A: Multiplying a Decimal by a Decimal Find the product. 0.3  0.4 0.3  0.4 0.12

  11. 3-5 Multiplying Decimals Multiply. Then place the decimal point. 2 decimal places + 1 decimal place 3 decimal places; use a placeholder zero Estimate the product. 0.8 is close to 1. Course 1 Additional Example 2B: Multiplying a Decimal by a Decimal 0.07  0.8 0.07  1 = 0.07 0.07  0.8 0.056 0.056 is close to the estimate of 0.07. The answer is reasonable.

  12. 3-5 Multiplying Decimals 2 decimal places Estimate the product. Round each factor to the nearest whole number. Multiply. Then place the decimal point. 3 decimal places + 1 decimal place Course 1 Additional Example 2C: Multiplying a Decimal by a Decimal 1.34  2.5 1  3 = 3 1.34  2.5 670 2680 3.350 3.350 is close to the estimate of 3. The answer is reasonable.

  13. 3-5 Multiplying Decimals Multiply. Then place the decimal point. 1 decimal place + 1 decimal place 2 decimal places Course 1 Check It Out: Example 2A Find the product. 0.5  0.2 0.5  0.2 0.10

  14. 3-5 Multiplying Decimals Multiply. Then place the decimal point. 2 decimal places + 1 decimal place 3 decimal places; use a placeholder zero Estimate the product. 0.9 is close to 1. Course 1 Check It Out: Example 2B 0.03  0.9 0.03  1 = 0.03 0.03  0.9 0.027 0.027 is close to the estimate of 0.03. The answer is reasonable.

  15. 3-5 Multiplying Decimals 2 decimal places Estimate the product. Round each factor to the nearest whole number. Multiply. Then place the decimal point. 3 decimal places + 1 decimal places Course 1 Check It Out: Example 2C 3.80  3.3 4  3 = 12 3.80  3.3 1140 11400 12.540 12.54 is close to the estimate of 12. The answer is reasonable.

  16. 3-5 Multiplying Decimals Remember! These notations all mean multiply 3 times x. 3 •x 3x 3(x) 3 decimal places + 0 decimal places 3 decimal places Substitute 3.062 for x. Course 1 Additional Example 3A: Evaluating Decimal Expressions Evaluate 5x for the value of x. x = 3.062 5x = 5(3.062) 3.062  5 15.310

  17. 3-5 Multiplying Decimals 2 decimal places + 0 decimal places 2 decimal places Substitute 4.79 for x. Course 1 Additional Example 3B: Evaluating Decimal Expressions Evaluate 5x for the value of x. x = 4.79 5x = 5(4.79) 4.79  5 23.95

  18. 3-5 Multiplying Decimals 3 decimal places + 0 decimal places 3 decimal places Substitute 2.012 for x. Course 1 Check It Out: Example 3A Evaluate 5x for the value of x. x = 2.012 5x = 5(2.012) 2.012  5 10.060

  19. 3-5 Multiplying Decimals 2 decimal places + 0 decimal places 2 decimal places Substitute 6.22 for x. Course 1 Check It Out: Example 3B Evaluate 5x for the value of x. x = 6.22 5x = 5(6.22) 6.22  5 31.10

  20. 3-5 Multiplying Decimals Course 1 Insert Lesson Title Here Lesson Quiz Find each product. 1. 0.8 2. 0.006  0.07 Evaluate 8x for each value of x.  0.07 0.056 0.00042 3.x = 2.705 4.x = 0.804 6.432 21.64 5. “Pick your own” peaches sell for $0.95 per pound. You picked 92 pounds of peaches. How much were you charged? $87.40

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