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Lesson 2-3
Estimate or Exact Answer
Beverly and her father are going to build a sand box. They need $46 for lumber, $11 for nails, and $72 for
sand. About how much money do they need for the sand box?
Understand
What facts do you know?
The lumber costs $46.
The nails cost $11.
The sand costs $72.
What do you need to find?
Find about how much money they need to build the sand box.
Plan
Since the question asks about how much money is needed, you can estimate the sum.
Solve
Round each amount to the nearest ten. Then add.
$46 → $50
$11 → $10
$72 → $70
$50 + $10 + $70 = $130
So, about $130 is needed to build the sand box.
Check
Look back at the problem. Suppose the question asked for an exact answer.
$46 + $11 + $72 = $129
Since $129 is close to $130, an estimate of $130 is correct.