2. Place value can help you understand and write and compare decimal numbers. Rounding Decimals

4. Look at the digit to the right of the place to which you are rounding. If it is 5 or greater, round up. If it is less than 5, round down. Caution! Rounding Decimals

5. Rounding Decimals to Estimate Sums and Differences Estimate by rounding to the indicated place value. A. 7.13 + 4.68; ones B. 9.705 – 0.2683; tenths 7.13 + 4.68 Round to the nearest whole number. 7 + 5 = 12 The sum is about 12. 9.705 9.7 Round to the tenths.Align. 9.4 Subtract. – 0.2683 –0.3 Rounding Decimals

6. Example Estimate by rounding to the indicated place value. 6.09 + 3.72; ones 6 + 4 = 10 Rounding Decimals

7. Compatible numbers are close to the numbers that are in the problem and are helpful when you are solving the problem mentally. Ex. 34.5 -> 35 2.95 -> 3Remember! Rounding Decimals

8. Using Compatible Numbers to Estimate Products and Quotients Estimate each product or quotient. A. 33.83  1.98 B. 72.77 ÷ 26.14 35  2 = 70 35 and 2 are compatible. 75 ÷ 25 = 3 75 and 25 are compatible. So, 72.77 ÷ 26.14 is about 3. So 33.83  1.98 is about 70. Rounding Decimals

9. Example Estimate each product or quotient. 62.31 ÷ 18.52 60 ÷ 20 = 3 Rounding Decimals

10. You can also use front-end estimation to estimate with decimals. Front-end estimation means to use only the whole-number part of the decimal. Rounding Decimals

11. Using Front-End Estimation Estimate a range for the sum. 7.86 + 36.97 + 5.40 Use front-end estimation. 7.86 7 Add the whole numbers only. 36.9736 The whole-number values of the decimals are less than the actual numbers, so the answer is an underestimate. 5.40+ 5 at least 48 The exact answer of 7.86 + 36.97 + 5.40 is greater than 48. Rounding Decimals

12. Example - Continued You can estimate a range for the sum by adjusting the decimal part of the numbers. Round the decimals up to 0.5 or 1. 0.861.00 Add the adjusted decimal part of the numbers. 0.971.00 Add the whole-number estimate and this sum. 0.40 + 0.50 2.50 48.00 + 2.50 = 50.50 The adjusted decimals are greater than the actual decimal, so 50.50 is an overestimate. The estimated range for the sum is from 48.00 to 50.50. Rounding Decimals

13. Check It Out Estimate a range for the sum. 8.92 + 47.88 + 3.41 underestimate: 8 + 47 + 3 = 58 overestimate: 9 + 48 + 3.5 = 60.5 from 58.00 to 60.50 Rounding Decimals

14. Lesson Quiz Estimate each product or quotient. 3 14 80 cm 3. 6.75  1.82 4. 10.5 ÷ 3.42 5. The snowfall in December, January, and February was 18.26 cm, 29.36 cm, and 32.87 cm, respectively. About how many total centimeters of snow fell during the three months? Estimate by rounding to the indicated place value. 3 4.5 1. 3.07442 + 1.352; tenths 2. 7.305 – 4.12689; nearest whole number Rounding Decimals

15. 1. Estimate by rounding to the indicated place value. 5.891+9.326; hundredths A. 14.21 B. 14.22 C. 15.21 D. 15.22 Student Response Systems Rounding Decimals

16. 2. Estimate by rounding to the indicated place value. 29.35-17.92; nearest whole number A. 10 B. 11 C. 12 D. 13 Student Response Systems Rounding Decimals

17. 3. Identify the estimate of the product of 16.77  3.81. A. 48 B. 51 C. 64 D. 68 Student Response Systems Rounding Decimals

18. 4. Identify the estimate of the quotient of 17.43  3.91. A. 6 B. 5 C. 4 D. 3 Student Response Systems Rounding Decimals

19. 5. The weight of three students in a class are 48.23 pounds, 54.81 pounds, and 45.3 pounds. Identify the total weight of the students. A. 130 lb B. 140 lb C. 150 lb D. 160 lb Student Response Systems Rounding Decimals