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Compare
Estimation to Actual Results of Computations
Estimate
to find a number close to an
exact answer.
Rounding is
one way to estimate. Then complete computation and compare results.
If
the digit to the right of the place you are rounding is
less
than 5, round down
 ; if it is 5 or greater, round up . |
Example 1
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 Nicole's
golf team is selling pens for a fund raising project. They
sold 187 pens for 25 cents each.
Are their total sales closer to $20, $30, $40, $50, or $60?
How can estimating help you solve
the problem?
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You know that 4 x 25 =
100, so 4 x $0.25 = $1.00.
Every dollar earned represents 4 pens sold.
You can round 187 to 200.
$200 divided by 4 = $50
Their total sale is closer to $50.
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Actual
Results
187 x $0.25 = $46.75 |
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Compare to
actual results
$46. 75 is close to $50.00 |
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Example 2
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 Mary
is buying supplies to make a window planter. She wants to make 2
of them. She has $10 to spend. Can she afford to buy 2 clay pots,
enough soil for the pots, and flowers?
Potting
soil $0.99
one bag fills 2 pots |
Pots
$1.49 |
Flowers
$1.99 |
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Step
1: It is easier
to add the prices if you round them to the nearest 10 cents.
Rounding will give you the following:
Potting soil = $1.00
Pots
= $1.50
Flowers = $2.00
Step
2: Next multiply
and add the rounded prices to find out what she can buy with
$10.00.
Potting soil: 1 x $1.00 = $1.00
Pots:
2 x $1.50 = $3.00
Flowers: 2x $2.00 = $4.00
Total:
$8.00
The items cost about $8.00, which is
less than $10.00.
Actual
Results
$0.99 + $1.49 +
$1.49 + $1.99 = $1.99 = $7.95
Compare to
actual results
$7.95 is close to
$8.00 |
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Is
your answer reasonable? Make estimates to compare to actual
results. |
Let's Practice!
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