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How do you Estimate Whole Numbers Using Rounding and Compatible Numbers?

How do you Estimate Whole Numbers Using Rounding and Compatible Numbers?. Sometimes in math you do not need an exact answer. Instead, you can use an estimate. Estimates are close to the exact answer but are usually easier and faster to find.

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How do you Estimate Whole Numbers Using Rounding and Compatible Numbers?

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  1. How do you Estimate Whole Numbers Using Rounding and Compatible Numbers?

  2. Sometimes in math you do not need an exact answer. Instead, you can use an estimate. Estimates are close to the exact answer but are usually easier and faster to find. When estimating, you can round the numbers in the problem to compatible numbers. Compatible numbers are close to the numbers in the problem, and they can help you do math mentally.

  3. Remember! • When rounding, look at the digit to the right of the place to which you are rounding. • If that digit is 5 or greater, round up. • If that digit is less than 5, round down.

  4. Round 12,345 down. Round 62,167 down. Estimate the sum by rounding to the place value indicated. 12,345 + 62,167; ten thousands 10,000 + 60,000 __________ 70,000 The sum is about 70,000.

  5. Round 4,983 up. Round 2,447 down. Estimate the difference by rounding to the place value indicated. 4,983 – 2,447; thousands 5,000 – 2,000 __________ 3,000 The difference is about 3,000.

  6. Round 13,235 down. Round 41,139 down. Estimate the sum by rounding to the place value indicated. 13,235 + 41,139; ten thousands 10,000 + 40,000 __________ 50,000 The sum is about 50,000.

  7. Round 5,723 up. Round 1,393 down. Estimate the difference by rounding to the place value indicated. 5,723 – 1,393; thousands 6,000 – 1,000 __________ 5,000 The difference is about 5,000.

  8. An estimate that is less than the exact answer is an underestimate. An estimate that is greater than the exact answer is an overestimate.

  9. Overestimate the number of softball members. The actual number of softball members is less than 160. Chelsea is planning the annual softball banquet for the 8 teams in the region. Each team has 18 members. Estimate how many plates she will need to buy if all the members attend. Find the number of softball members. 8 18 8 20 8  20 = 160 Chelsea should buy about 160 plates.

  10. Overestimate the number of teams. The actual number of softball members is less than 180. Another method Find the number of softball members. 10 18 10 18 10  18 = 180 Chelsea should buy about 180 plates.

  11. Overestimate the number of students. The actual number of students is less than 150. Ms. Oliver wants to buy the entire seventh-grade new pencils. There are 5 seventh-grade homeroom classes of 28 students. Estimate how many pencils Ms. Oliver needs to buy for all of the students. Find the number of students in the seventh grade. 5 28 5 30 5  30 = 150 Ms. Oliver should buy about 150 pencils.

  12. 240 and 60 are compatible numbers. Underestimate the speed. Because he underestimated the speed, the actual time will be less than 4 hours. Estimating a Quotient Using Compatible Numbers Mr. Douglas will drive 243 miles to the fair at 65 mi/h. About how long will his trip take? 243 ÷ 65 240 ÷ 60 240 ÷ 60 = 4 The trip will take about 4 hours.

  13. 100 and 50 are compatible numbers. Underestimate the speed. Because she underestimated the speed, the actual time will be less than 2 hours. Mrs. Blair will drive 103 miles to the airport at 55 mi/h. About how long will her trip take? 103 ÷ 55 100 ÷ 50 100 ÷ 50 = 2 The trip will take about 2 hours.

  14. Lesson Quiz Estimate each sum or difference by rounding to the place value indicated. 1. 7,420 + 3,527; thousands 2. 47,821 + 19,925; ten thousands 3. 8,254 – 5,703; thousands 4. 66,845 – 24,782; ten thousands 5. One quart of paint covers an area of 100 square feet. How many quarts are needed to paint a wall 8 feet tall and 19 feet wide?

  15. Lesson Quiz Answers Estimate each sum or difference by rounding to the place value indicated. 1. 7,420 + 3,527; thousands 2. 47,821 + 19,925; ten thousands 3. 8,254 – 5,703; thousands 4. 66,845 – 24,782; ten thousands 5. One quart of paint covers an area of 100 square feet. How many quarts are needed to paint a wall 8 feet tall and 19 feet wide? 11,000 70,000 2,000 50,000 2

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