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Estimation
Subject: Mathematics
Grade: 35
Brief Description
Students estimate the cost of individual items found on a typical grocery list.
Objectives
Students estimate the cost of individual items found on a typical grocery list; for example, apples, bananas, and carrots. Students estimate the total cost of all items on a typical grocery list.
Keywords
estimation, estimating, grocery, list Materials Needed
 book Betcha!: Estimating (Mathstart, Level 3), by Stuart J. Murphy
 an overhead projector
 a transparency listing key words and definitions
 a chart of currency and coinage
 40 grocery items with prices or grocery flash cards with prices
 four teachercreated grocery lists with ten grocery items on each
 four grocery baskets or other baskets with handles
 four grocery bags
 writing paper
 pencils
Lesson Plan
 Explain to students that today they will learn to estimate the cost of various items on a grocery list and use these estimations to get the total estimated cost of a grocery list.
 Read to the class the book Betcha!: Estimating (Mathstart, Level 3), and explore the estimation strategies of the two boys in the story.
 Express the importance of estimating in everyday life; for example, ordering supplies, evaluating cost of trips, and preparing refreshments for a party.
 On the board, write a few two and threedigit addition problems with decimals to refresh students' skills, and then build on that to explain when they are appropriately used in total cost estimation.
 Display on the overhead projector the transparency with the meanings of the words addends, approximate, estimate, and guessing.
 Use the chart of currency and coinage to review the relationships of pennies, nickels, dimes, quarters, and dollars.
 Illustrate simple estimation problems using the chart information, for example, "Apples are 24 cents each; estimate the total cost of four apples."
 Draw a parallel between estimating the cost of an apple and estimating the cost of individual grocery items and a complete list of grocery items.
 Write the following word problem on the board or a transparency to illustrate cost estimation: "You are sent to the store to buy four apples for a pie. Each apple cost 24 cents. Estimate the total cost of the apples." Point out that each apple costs approximately one quarter.
 Show students the symbolic representation of the actual and estimated cost of the apples on the board ($.24 + $.24 + $.24 + $.24 = $.96 and $.25 + $.25 + $.25 + $.25 = $1).
 After sharing the word problem, check students' understanding by asking students to estimate the total cost of enough apples to make two pies.
 Quiz the children on their responses and the reason for those responses.
Guided Practice
 Place children into groups of four, and assign each child in each group a number: 1, 2, 3, or 4.
 Hand out to each group a grocery basket with ten items, a grocery bag, a grocery list, paper, and pencils.
 Instruct each group to remove the grocery items from the basket, and spread them out on a desk.
 Have each group read its grocery list and place those items in the basket.
 Say the following:
 "Student number 1, remove the first item on the grocery list from your grocery basket. Now estimate the cost of that item. Write the estimate down on your paper. Place the item in your grocery bag, and tell us the total estimated cost of your groceries at this point.
 "Student number 2, remove the next two items on the grocery list from your grocery basket. Now estimate the cost of each item. Write the estimates down on your paper. Place the items in your grocery bag, and tell us the total estimated cost of your groceries at this point.
 "Student number 3, remove the next three items on the grocery list from your grocery basket. Now estimate the cost of each item. Write the estimates down on your paper. Place the items in your grocery bag, and tell us the total estimated cost of your groceries at this point.
 "Student number 4, remove the last four items from your grocery basket. Now estimate the cost of each item. Write the estimates down on your paper. Place the items in your grocery bag, and tell us the total estimated cost of your groceries at this point."
 Bring the session to a close by having students orally relate their estimation problems with their total estimates.
Extension
 Ask each group to make up its own grocery list of five items.
 Have students write down the estimate of each item and the total cost of their groceries.
 Observe the activity in case someone needs help.
Variations
1. Strategies to use with exceptional children:
 For enrichment, increase the number of grocery items given to each group.
 For remediation, allow students to use items with costs that are easy to estimate ($.9, $.19, $.24, $.49, etc.).
2. Activities that value cultural diversity:
 Ask students who speak English as a second language to give their estimations to the class in their primary language.
 Ask students from other cultures to bring several small grocery items from home related to the culture to make estimations.
3. Activities that foster active inquiry, critical thinking, and problem solving:
 Ask students to bring objects from home to use in the next day's lesson to display estimation problems. Some items might include marbles or dry beans. Have students use the objects to make up problems such as these:
 Ten marbles cost $.95; estimate the cost of 50 marbles.
 A bag of 50 dry beans costs $.23; estimate the cost of two bags.
 Arrange a class field trip to a grocery store to see the many practical applications for estimation. Encourage students to notice the various costs of items on the shelves. Ask each student to estimate the cost of two boxes of his or her favorite cereal.
Assessment
Have students estimate the cost of all the items on a grocery list you design and get a total cost of those items at an accuracy rate of at least 80 percent.
Lesson Plan Source
Submitted By
Chris McKeever ([email protected]), Athens State University, Nauvoo, Alabama
As our highlighted lesson, the submitter was awarded a $50 honorarium. See our guidelines to submit yours!
03/15/2001
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