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Sometimes it makes more sense to underestimate.
Sometimes an overestimate is more reasonable.

Solve the problem using the flowchart.

Lisa wants to buy a shirt that costs $9.95 and a sweater that costs $18.25. She has  $13.20 that she has saved and $25.40 from baby-sitting. Does she have enough money?


Use the flowchart below to choose and apply estimation methods.





Underestimate, round down.

To be sure that Lisa has enough money, underestimate. 
You want your estimate to be less than what Lisa actually has.
Round down the money she has.





$10 + $20 




Overestimate, round up.

Overestimate the cost of the shirt and sweater. This way your estimate will be more than the actual cost.

Round up the cost of the shirt and sweater.

$9.95  $10.00
$18.25  $19.00 

$10 + $19 

= $29.00
Since Lisa has about $30 and the shirt and sweater cost about $29, she has enough money.

Read all the information to determine whether to underestimate or overestimate. Then find the facts you need.
To Underestimate, round down.
To Overestimate, round up.

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