The student will identify appropriate uses for estimation.
The student will round purchase prices to estimate total
purchases in a school store setting.
The student will practice estimating by using rounding and
mental computations to arrive at estimates.
Connection to Bloom’s Taxonomy
- Clear Jar ( or other container )
- Crayons or Colored Pencils
- Dictionary ( Printed and/or on the Web )
Happy Cap Erasers ( or any other small sized school store item
appropriate for estimating quantity )
- Index Cards
- Item Cards from the Geddes Kit List
- Worksheets for lesson plan 4 (see sidebar)
What is an estimate?
Ask several students to use a dictionary or on-line dictionary
to define the word “estimate.” Record several of those
definitions on the board. In general, an estimate is an
approximate calculation. Use
Word Origin by Hannie in the sidebar for
Ask students to think about times when they may use estimating
outside of the classroom.
Have you ever purchased something on sale?
What does it mean to buy something on sale?
Have students brainstorm responses to the following two
questions. Some possible responses may include:
To determine how long it will take to drive somewhere
To determine how long it will take to complete a homework
To determine how much time will be needed to complete a
project at work or home
To determine how much money to bring to the grocery store to
purchase a week’s worth of food
To determine what time to set the alarm clock based on how
long it will take to get ready in the morning
To determine how many suitcases to pack for a week-long family
To determine how much gasoline will be needed to fill the car
To determine a weekly or monthly budget for household expenses
- To determine how much food to prepare for a party
Discuss why estimation is useful and explain to students the
overall purpose of estimation. Students should understand that
estimates provide approximations or reasonable answers to
questions. Although the exact amount or number might not be
known, an estimate helps to plan and prepare. Estimates actually
help people to solve problems. The world around us is filled
with unknowns. We do not and will not always know or have the
exact answer to a question or problem. However, estimates
provide people with a way of making reasonable, intelligent
approximations when the exact answer is not easily or readily
Exploring and Learning
Fill a jar with Happy Cap Erasers or any other small-sized
school store item. Show a single item to students so that they
have an idea as to the item’s shape and size. Then show the
class the filled jar of erasers and ask them to estimate the
number of erasers or items in the jar. Record student
estimations on the board.
As a class, look at the list of estimates and determine if
there was a wide range of estimates or were the numbers fairly
close to one another.
Discuss how estimates are derived by asking students to share
their approaches, thought processes, and methods for
developing their estimates. Often estimates are developed
based on prior knowledge, rough calculations, or simply an
Explain that estimating is very useful when making purchases.
It is a helpful way to calculate quickly the total amount to
be purchased and to ensure you have enough money for your
Estimating Store Purchases - Guided Practice (PDF)
as a transparency to help guide students through the process
of estimation. Explain to students that making estimates in a
store may involve rounding, mental calculations, or using
paper and pencil to do quick calculations. It is often better
to estimate a little higher to ensure that you have enough
money to afford the purchase.
Present students with the following scenario:
RG and Hannie are purchasing for their Raymond Geddes
Elementary School Store. Today in math class, they learned
about estimation and want to practice what they have
learned for the school store. RG and Hannie will help
estimate the total price of two different purchases. With
this information, the students will know whether or not
they have enough money to buy what they want to sell at
the school store. Sniffer will tabulate the exact total
price using a calculator.
Can you help RG, Hannie, and Sniffer estimate the
To help complete the scenario, pair students together and
provide them with a copy of
Estimate Store Purchases Worksheet (PDF). Explain and list on the board or as a transparency the
- Use rounding to generate an estimate for each item.
Use a calculator to determine the actual total price.
Does each student have enough money to make his/her
As a class, review the results and determine if Natalie and
Matt have enough money to make their purchases? Student
estimations should determine that Natalie does not have enough
money to purchase all the items that she wanted to buy. Review
with students Natalie’s 2 alternatives found on the
Estimate Store Purchases Worksheet Key (PDF).
The scenario involving Matt provides a different look at
estimation. Some students will overestimate Matt’s total
purchase price when rounding upward. Estimating by rounding
upward showed that Matt could not afford all his items.
However the actual price for all of his items was less than
the $75.00 he had to spend. Rounding each item’s price upward
yielded an overestimate. Review the upward estimation on the
Estimate Store Purchases Worksheet (PDF)
with students. Explain that when you are making purchases, it
is often better to overestimate than to underestimate the
total purchase price.
Provide students with additional practice at estimating
purchase totals by creating item cards using index cards and
Geddes Kit List (PDF). You can create up to 20 item cards, each containing the
item name and corresponding purchase price. For example, one
card will state “Retro Pencil $8.64/Display”. Fold the cards
in half and place them in a container.
Call two students to the front of the classroom to lead the
activity. One student will roll a die and the other will draw
an item card from the container. Divide the remainder of the
class into teams of 3-4 students. All students will
participate by estimating (using mental computation only) a
total purchase price within their assigned teams. Remind
students that you do not want the actual total price, but an
estimate. To estimate in this activity means to round the item
price first and then to multiply that price by the quantity
rolled on the die.
Ask each team to jot down their estimate. Students will share
their estimates aloud after each card is drawn and die rolled.
Did everyone arrive at the same estimate? If not, discuss any
differences in creating the estimate.
Extended Learning and Practice
Open up your own school store using the Geddes School Store
Kit and our
School Stores: An Operating Manual. Operating
a school store is an excellent opportunity for inquiry
based/hands-on learning that is both fun and rewarding. Create
an instant real life business in your classroom by using the
merchandise in the Geddes Kit and following the school store
operations manual. A school store will allow opportunity for
raising money, provides a service to students, and creates an
atmosphere of responsibility while building valuable team
working skills. This lesson demonstrated how customers use
estimation prior to making purchases. Identify several other
ways estimation can be used within a school store. Some
possibilities include: estimating and forecasting future sales
based on prior actual sales data, estimating the amount of
shelf space needed to display store items, or simply
estimating how much help will be needed to operate the store.
Challenge students by using two dice to perform mental
computations for each item card created in step 10 of the
Exploring and Learning component. Explain to students that
estimation is very helpful when the quantities increase and
you can begin to group by tens.
Have students think about what it means to overestimate versus
underestimate. Ask which do you think is better, and why.
Provide one or two examples to support your answer.
(U.S. Department of Education Archives) for additional
estimation activities that can be completed at the grocery
Figure This! Math Challenges for Families. The Challenge Index contains estimation challenges. This
website was developed by the National Council of Teachers of
Provide each student with an index card and have them answer the
following questions on one side of the index card:
What are two new things that you have learned?
What else would you like to learn about this topic?
On the back side of the index card, instruct the students to
draw a picture of something they learned about during this
lesson. The index cards can be hole punched and held together
with a simple shower curtain ring.