Estimating Products with Compatible Numbers

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​

​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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​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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