3-2 Estimating Decimals Warm Up Warm Up Lesson Presentation Lesson Presentation Problem of the Day Problem of the Day Lesson Quizzes Lesson Quizzes

3-2 Estimating Decimals Warm Up Order the decimals from least to greatest , 18.7, , 9.66, 9.6, Write each in words , 18.7, , 9.076, 9.6, 9.66 three and seventy-two thousandths six and one thousand two hundred fifty-eight ten-thousandths

3-2 Estimating Decimals Problem of the Day Calculate your age in months. Possible answer: 11 yr 8 mo = 140 mo

3-2 Estimating Decimals Vocabulary clustering front-end estimation

3-2 Estimating Decimals When numbers are about the same value, you can use clustering to estimate. Clustering means rounding the numbers to the same value.

3-2 Estimating Decimals Additional Example 1: Health Application Nancy wants to cycle, ice skate, and water ski for 30 minutes each. About how many calories will she burn in all? (Cycling = calories, ice skating = calories, and water skiing = calories) The addends cluster around To estimate the total number of calories, round each addend to Add. 510 Nancy burns about 510 calories.

3-2 Estimating Decimals Check It Out: Example 1 Abner wants to run, roller-skate, and snow ski for 60 minutes each. About how many calories will he burn in all? (Running = calories, roller-skating = calories, and snow skiing = calories.) 190 × 3 = 570 calories

3-2 Estimating 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!

3-2 Estimating Decimals Additional Example 2: 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

3-2 Estimating Decimals Check It Out: Example 2 Estimate by rounding to the indicated place value ; ones = 10

3-2 Estimating Decimals Compatible numbers are close to the numbers that are in the problem and are helpful when you are solving the problem mentally.Remember!

3-2 Estimating Decimals Additional Example 3: 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.

3-2 Estimating Decimals Check It Out: Example 3 Estimate each product or quotient ÷ ÷ 20 = 3

3-2 Estimating 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.

3-2 Estimating Decimals Additional Example 4: 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.

3-2 Estimating Decimals Additional Example 4 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

3-2 Estimating Decimals Check It Out: Example 4 Estimate a range for the sum underestimate: = 58 overestimate: = 60.5 from to 60.50

3-2 Estimating Decimals Standard Lesson Quiz Lesson Quizzes Lesson Quiz for Student Response Systems

3-2 Estimating 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

3-2 Estimating Decimals 1. Estimate by rounding to the indicated place value ; hundredths A B C D Lesson Quiz for Student Response Systems

3-2 Estimating Decimals 2. Estimate by rounding to the indicated place value ; nearest whole number A. 10 B. 11 C. 12 D. 13 Lesson Quiz for Student Response Systems

3-2 Estimating Decimals 3. Identify the estimate of the product of  A. 48 B. 51 C. 64 D. 68 Lesson Quiz for Student Response Systems

3-2 Estimating Decimals 4. Identify the estimate of the quotient of  A. 6 B. 5 C. 4 D. 3 Lesson Quiz for Student Response Systems

3-2 Estimating 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 Lesson Quiz for Student Response Systems