Mathematics
Grade 3
15 min
Estimate products - multiply by 1-digit numbers
Estimate products - multiply by 1-digit numbers
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1
Introduction & Learning Objectives
Learning Objectives
Define 'estimate' and 'product' in the context of multiplication.
Round 2-digit and 3-digit numbers to the nearest ten or hundred.
Use rounding to estimate the product of a 1-digit number and a 2-digit number.
Use rounding to estimate the product of a 1-digit number and a 3-digit number.
Multiply a 1-digit number by multiples of 10 and 100.
Explain why an estimated answer is useful for checking if a real answer is reasonable.
If a farmer has 7 rows of corn with 42 plants in each row, about how many corn plants does she have in total? 🌽 Let's find out how to make a smart guess!
In this lesson, you will learn how to estimate products. Estimating is a super-fast way to find an answer that is close to the exact answer. It helps you...
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Key Concepts & Vocabulary
TermDefinitionExample
EstimateAn answer that is close to the exact answer. It's like making a 'smart guess'. We often use the word 'about'.An estimate for 98 + 103 is 200, because 98 is close to 100 and 103 is close to 100.
ProductThe answer you get when you multiply two or more numbers.In 5 x 6 = 30, the product is 30.
RoundingMaking a number simpler by finding the closest 'friendly' number, like the nearest ten or hundred.The number 28 can be rounded to 30. The number 11 can be rounded to 10.
FactorA number that is multiplied by another number to find a product.In 5 x 6 = 30, the factors are 5 and 6.
Multiple of 10A number you get when you multiply 10 by any whole number. These numbers always end in a zero.10, 20, 30, 40, 50, 60...
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Core Formulas
The Rounding Rule
Look at the digit to the right of the place you are rounding to. If it is 5, 6, 7, 8, or 9, you round up. If it is 0, 1, 2, 3, or 4, you round down.
Use this rule to change a tricky number into a 'friendly' number (a multiple of 10 or 100) before you multiply.
The Estimation Process
Step 1: Round the larger factor. Step 2: Multiply the rounded factor by the 1-digit factor.
This is the main plan for estimating products. Always round first, then multiply second.
The 'Magic Zero' Trick
To multiply by a multiple of 10 (like 40), multiply by the first digit (4) and then add the zero to your answer.
This makes multiplying with rounded numbers easy. For example, for 7 x 40, think '7 x 4 = 28', then add the zero to get 280.
4 more steps in this tutorial
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Challenging
Maria is estimating the product of a 2-digit number and 7. Her estimated product is 210. The original 2-digit number was odd. Which of these could have been the original number?
A.26
B.29
C.32
D.35
Challenging
A store sells packs of stickers for $3 each. Each pack has 118 stickers. If you buy 5 packs, you get 50 bonus stickers. Which expression shows the best way to estimate the total number of stickers you would get?
A.100 x 5
B.120 x 5
C.(120 x 5) + 50
D.118 x 5
Challenging
The product of a 2-digit number and 9 is estimated to be 360. The exact product is 342. What was the original 2-digit number?
A.35
B.37
C.42
D.38
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