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Decimals Percent Multiplying decimals Dividing decimalsHere is everything you need to know about estimation for. You’ll learn the definition of estimation and how to use various estimation strategies to make calculations quicker and easier.
Students will first learn about estimation in 3rd grade math as part of their work with operations and algebraic thinking. They will expand upon that knowledge as they progress through elementary math.
Estimation is when you use approximate values in a calculation to give an approximate answer rather than an exact answer.
Estimation helps to make calculations quicker and easier.
Let’s look at some estimation strategies.
Estimation strategy – Rounding 

Rounding the decimal numbers to the nearest whole number (or nearest ten, Estimate the value of
5.7 \times 6.3
Round 6.3 to the nearest whole number. 6 \times 6 is an easier calculation to make than 5.7 \times 6.3.

Estimation strategy – Compatible Numbers 

Compatible numbers are pairs of numbers that work well together, they can be
Estimate the value of 2160 \div 29

How does this relate to 4th grade math and 5th grade math?
In order to estimate using compatible numbers.
In order to estimate using rounding.
In order to estimate a real world scenario using rounding or compatible numbers.
Use this quiz to check your grade 3 to 5 students’ understanding of rounding numbers. 10+ questions with answers covering a range of 3rd, 4th, and 5th grade rounding numbers topics to identify areas of strength and support!
DOWNLOAD FREEUse this quiz to check your grade 3 to 5 students’ understanding of rounding numbers. 10+ questions with answers covering a range of 3rd, 4th, and 5th grade rounding numbers topics to identify areas of strength and support!
DOWNLOAD FREEEstimate the value of 228 \times 19 by using compatible numbers.
228 is close to 220.
19 is close to 20
2Create the new calculation using the compatible numbers.
220 \times 20 =
This calculation is much easier to do than 228\times 19.
3Do the calculation(s) using the rounded numbers of the compatible numbers to give an approximate answer, using the ‘approximately equal to’ symbol \textbf{≈}
220\times20=4400
228\times19=4,332
228\times19\approx4,400
Estimate the value of 2774\div73
Round each number so that they are compatible.
2774 is close to 2800.
73 is close to 70.
Create the new calculation using the compatible numbers.
2800\div70
Do the calculation using the compatible numbers to give an approximate answer, using the ‘approximately equal to’ symbol \textbf{≈}
2800\div70=40
2774\div73=38
2774\div73\approx40
Estimate the value by rounding to the nearest whole number.
6.9\times 9.6
Round each number in the calculation the nearest whole number, nearest ten, nearest hundred, or nearest thousand.
6.9 rounded to the nearest whole number is 7. \;\; 9 > 5 so round up by adding 1 to the rounded digit. 6 + 1 = 7
9.6 rounded to the nearest whole number is 10. \;\; 6 > 5, so round up by adding 1 to the rounded digit. 9 + 1 = 10
Create the calculation using the rounded numbers.
7\times10=
This calculation is much easier to do than 6.9\times9.6
Do the calculation using the rounded numbers to give an approximate answer, using the ‘approximately equal to’ symbol \textbf{≈}
7\times10=70
6.9\times9.6=66.24
6.9\times9.6\approx70
Estimate the value by rounding to the nearest whole number.
783.12\div2.4
Round each number in the calculation the nearest whole number, nearest ten, nearest hundred, or nearest thousand.
783.12 round to the nearest ten. 3 < 5, so round down by leaving the rounded digit alone. The number will round to 780.
2.4 round to the nearest whole number. 4 < 5, so round down by leaving the rounded digit alone. The number will round to 2.
Create the calculation using the rounded numbers.
780\div2
Do the calculation using the rounded numbers to give an approximate answer, using the ‘approximately equal to’ symbol \textbf{≈}
780\div2=390
783.12\div 2.4 = 326.3
783.12\div2.4\approx390
Benny has saved \$127.54. Sandy has saved 2.5 times as much money as Benny.
Estimate how much money Sandy has saved.
Read the problem and decide which operation(s) to use.
Multiplication will be used to solve this problem.
Create an equation.
127.54\times2.5= \; ?
Use rounding or compatible numbers to write a new equation.
Rounding strategy will be used.
127.54 round to the nearest ten. 7 > 5, so round up by adding one to the rounding digit. 2 + 1 = 3, so it will round to 130.
2.5 rounded to the nearest whole number is 3. \; 5 = 5, so round up by adding one to the rounded digit.
130\times3=?
Do the calculation(s) using the rounded numbers of the compatible numbers to give an approximate answer, using the ‘approximately equal to’ symbol \textbf{≈}
130\times3=390
127.54\times 2.5 = 318.85
127.54\times2.5\approx390
Label the answer.
Sandy saved approximately \$390.
Janna has \$21.16. She wants to buy the large candy bars for her party. The large candy bars cost \$1.84. Estimate how many large candy bars she can buy.
Read the problem and decide which operation(s) to use.
Division is the operation that will be used.
Create an equation.
21.16\div 1.84=
Use rounding or compatible numbers to write a new equation.
21.16 round to the nearest ten. 1 < 5, so round down by leaving the rounded digit alone. The number will round to be 20.
1.84 round to the nearest whole number. 8 > 5, so round up by adding 1 to the rounded digit. 1 + 1 = 2. The number will round to be 2.
Do the calculation(s) using the rounded numbers of the compatible numbers to give an approximate answer, using the ‘approximately equal to’ symbol \textbf{≈}
20\div 2 = 10
21.16\div1.84 = 11.5
21.16\div1.84\approx 10
Label the answer.
Janna can buy approximately 10 large candy bars.
1. Use compatible numbers to estimate the value of 22\times 19?
22 is close to 20
19 is close to 20
20\times20 = 400
22\times 19\approx 400
The actual answer is 418 which is close to 400.
2. What are the appropriate compatible numbers to estimate the value of 219\div74
220 and 70
200 and 70
210 and 70
220 and 75
Compatible numbers are a pair of numbers that work well together.
In this case, estimating 219 to be 210 and estimating 74 to be 70 will make a pair of compatible numbers. 210\div30 is easy and quick to calculate.
The compatible numbers are 210 and 70.
3. Estimate the value of 7.2 \times 98 using rounding.
7.2 rounded to the nearest whole number is 7. \;\; 2 < 5 , so round down by leaving the rounding digit alone.
98 rounded to the nearest hundred is 100. \;\; 8 > 5, so round up by adding 1 to the rounded digit.
7\times100=7007.2\times98\approx700
4. Estimate the value of 389\div81 using rounding.
389 round to the nearest hundred. 8 > 5, so round up by adding one to the rounded digit. 3 + 1 = 4, so 400.
81 round to the nearest ten. 1 < 5, so round down by leaving the rounding digit alone.
400 \div 80 = 5
389 \div 81 \approx{5}
5. Jenny has saved \$114.65 in her savings account. Brandon has saved 1.5 times the amount of money. Estimate the amount of money Brandon has saved.
You will estimate the value of 114.65\times 1.5.
Round \$114.65 to the nearest ten. 4 < 5 so leave the rounded digit alone, so it will round to be \$110. \; 1.5 round to the nearest whole number. 5 = 5, so round up by adding one to the rounded digit. 1 + 1 = 2.
\$110\times2=\$220
\$114.65\times1.5\approx \$220
6. There are 678 boxes in 11 storage spaces. Estimate how many boxes there are in 1 storage space by rounding the values to the nearest ten.
\approx{57} boxes
\approx{68} boxes
\approx{64} boxes
\approx{58} boxes
You will estimate the value of 678\div11.
Round 678 to the nearest ten. 8 > 5, round up by adding 1 to the rounded digit. 7 + 1 = 8, so the rounded number is 680.
Round 11 to the nearest ten. 1 < 5, leave the rounded digit alone, so the rounded number is 10.
680\div10=68
678\div11\approx68
Rounding is taking a number and rounding it to a specific place, for example rounding to the nearest tens place, nearest hundreds place, nearest hundredths place, etc.. Compatible numbers are numbers that work well with each other.
There is no right or wrong way to estimate. In many cases it depends on the actual problem.
Round to the place that will make the calculations the easiest to do.
The closer your estimated answer is to the exact answer, the better the estimate.
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Prepare for math tests in your state with these Grade 3 to Grade 6 practice assessments for Common Core and state equivalents.
40 multiple choice questions and detailed answers to support test prep, created by US math experts covering a range of topics!