Estimating Products and Estimating Quotients

Estimating with Whole Numbers

By Ron Schroeder

Vocabulary

Estimate - close to the exact answer but are usually easier and faster to find.

Compatible numbers - close to the numbers in the problem, and they can help you do math mentally.

Underestimate - an estimate that is less than the exact answer.

Over estimate - an estimate that is greater than the exact answer.​

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5,439 + 7,516; thousands

5,000 + 8,000 = 13,000

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Sometimes in math you do not need the exact answer. you can estimate, instead.

​Estimate each by rounding to the place value indicated.

​62,167 - 47,511: ten thousands

60,000 - 50,000 = 10,000​

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Estimate the sum by rounding to the place value indicated.

4,689 + 2,469: thousands

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Estimate the difference by rounding to the place value indicated.

50,498 - 35,798: ten thousands

​Estimating a product by rounding

Ms. Doran is planning a graduation celebration for the entire eighth grade. There are 3 eighth-grade homeroom classes of 28 students. Estimate how many cups ms. Dorn needs to buy for the celebration.

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we need to find the number of students in the eighth grade.

3 x 28→​ 3 x 30 Overestimate the number of students.

9 x 30 = 270​ If she buys 270 cups, she will have enough for every student

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In three bicycle races last year there were 290 bottles of water used in May, 590 bottles of water used in August, and 180 bottles of water used in November. If the same number of riders enter the races each year, estimate the number of bottles that will be needed for races held in May over the next five years.

​Estimating a quotient using compatible numbers

Mrs. Smith will drive 130 miles to take James to the state fair. She can drive 70 mph. About how long will the trip take?

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To find how long the trip will take, divide the miles by the miles per hour.

miles ÷​ mph

130 ÷​ 70 → 130 ÷ 65 130 and 65 are compatible numbers.

130 ÷​ 65 = 2 It will take Mrs. Smith about 2 hours to reach the state fair

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Samantha drives 120 miles on her scooter. If the scooter gets about 63 miles per gallonof gas, about how many gallons of gas did she use?