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

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

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

Example Estimate by rounding to the indicated place value ; ones = 10 Rounding Decimals

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

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

Example Estimate each product or quotient ÷ ÷ 20 = 3 Rounding Decimals

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

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

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 Add the adjusted decimal part of the numbers Add the whole-number estimate and this sum = The adjusted decimals are greater than the actual decimal, so is an overestimate. The estimated range for the sum is from to Rounding Decimals

Check It Out Estimate a range for the sum underestimate: = 58 overestimate: = 60.5 from to Rounding Decimals

Lesson Quiz Estimate each product or quotient cm  ÷ The snowfall in December, January, and February was cm, cm, and cm, respectively. About how many total centimeters of snow fell during the three months? Estimate by rounding to the indicated place value ; tenths – ; nearest whole number Rounding Decimals

1. Estimate by rounding to the indicated place value ; hundredths A B C D Student Response Systems Rounding Decimals

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

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

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

5. The weight of three students in a class are pounds, 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