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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.