ESTIMATION
Three Types of Estimation
1. Measurement Estimation
2. Quantity Estimation
3. Computational Estimation
1. If I can drive 326 miles on 15 gallons of
gasoline what is my approximate mpg?
2. Is 10 dollars enough to buy 5 drinks that cost
$2.19 each?
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A Computational Estimate
• Determine a number that is the approximation of a
computation.
• Not a guess, involves some form of reasoning.
• Sometimes knowing if the result is more or less
than a number is sufficient.
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Multi-Digit Numbers
1. Can be built upon or taken apart in a wide
variety of ways.
2. Use easier-to-handle parts of numbers to
create estimates.
3. Computation can then be done mentally.
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Multi-Digit Numbers
1. Substitute “nice” numbers for hard ones
2. Computation can then be done mentally.
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Computational Estimation
1. Use a variety of strategies developed over
time
2. Find Real Examples of Estimation
3. Accept a Range of Estimates
4. Focus on Flexible Methods NOT Answers
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Understanding
Computational Estimation
Use the Language of Estimation
“About” “Close”
“Just about”
“A little more than”
“A little less than”
“Between””
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Understanding
Computational Estimation
Estimating Without Estimates
Over or Under?
37+75 Over or Under 100
712-458 Over or under 300
319/45 Over or under 6
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Understanding
Computational Estimation
Estimating Without Estimates
High or Low
736 x 18
750 x 10 730 x 15
700 x 20 750 x 20
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Computational Estimation
Strategies
Three methods for Computational Estimation
Front End
Rounding
Compatible (nice/friendly) Numbers
In all three--make an initial estimate and then adjust if need be.
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Front End Methods
487 + 31 + 710
400+0+700=1100
Adjust to 1200
421/59
400/60=less than 7
Adjust to 7
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Rounding Methods
$48.17+$1.89+$24.95
$50+$0+$20=70
Adjust to $72
$4.17 x 6
$4 x 6 = $24
Adjust $25
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Compatible Numbers
41+29+63+17+65+85
41+63=about100
29+65=about 100
17+85=about 100
300-adjust to a bit more
than 300
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Compatible Numbers
371/21
400/20=20
Adjust to a few less than 20
69-27
67-27=40
Adjust to a bit more than 40
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Estimating with Fractions,
Decimals, and Percents
Represent Most Real-World Estimations
Connect to Computational Skill Development
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