help the students become more familiar with the set model for
subtraction, ask them to watch as you show six pasta shapes in your
hand. Tell them you are going to play "Guess How Many?" Then put your
hands behind your back, transferring some, say four, of the pasta
shapes to your other hand. Ask a volunteer which hand to show, and then
bring that hand forward, opening it so the pasta shapes are visible.
Now ask the students to "guess" how many pasta shapes are in your other
hand and then count to verify their guess. Then give the students a
chance to play this game with one another. [This activity involves a
missing addend situation (6 - __ = 4) in concrete form.] Note:
This concept involves abstract thinking that may be too challenging for
some students. Other students may need to divide manipulatives of their
own into two sets to answer the question.
Now place the students in pairs and provide them with pasta shapes
and a piece of paper for a workmat. Tell them that they will be telling
take-away stories and then using pasta shapes to model the stories.
Remind them to record how many they started with, how many they took
away, and how many were left using either the vertical or horizontal
format practiced in the previous lesson. Note:
Students generally find the vertical format easier to use, so you may
wish to suggest this format to the students who are more challenged by
To model the process, call on a volunteer to start a story that
involves a number that is 10 or less. For example, a set of seven birds
were at the feeder. Ask the students to show the corresponding number
of pieces of pasta on their paper plate. Then call on another volunteer
to continue the story by adding a sentence that involves taking away.
For example, a set of three birds flew away. Invite the students to
take away the mentioned number of pasta pieces. Then ask, "How many
pieces of pasta are on your plate now?" [In the example, four.] Ask the
students what that number is called. [The difference.] Now call on a
volunteer to record the subtraction in the horizontal format. Ask
another volunteer to record the subtraction in the number sentence in
vertical format. Repeat with another story until the students are
comfortable with the process. Give the pairs time to tell and record at
least two stories.
Another example includes the following:
Mary made 5 heart shaped cookies. She ate 2 of them. How many cookies are left?
Then tell them they will record subtraction in another way--in chart form. Distribute the Take-Away Activity Sheet, to the pairs.
Ask them to point to the column labeled “Number of Pasta
Shapes.” Then ask them to read the titles of the other two columns.
Call on a volunteer to make up a story problem. Guide the students in
recording values in the first two columns. Ask another student to tell
what should be written in the “Number Left” column. Now have the
students work together to create new entries for the chart. Encourage
them to model each trio of entries with pasta shapes. After they have
had time to create several rows on their charts, call the students
together and ask them to share one of the rows that they have written.
|Number of |
| || || |
| || || |
As you discuss their entries, you may wish to review the terms
“take away” and “difference.” If no student shares a row where zero is
taken away, ask the class what would be recorded if you started with
five pasta shapes and took zero pieces away. Encourage the students to
act this operation out with their pasta shapes and record the result on
their charts. Repeat with a model for a difference of 0. Prompt the
students to add this entry to their chart as well.
Now ask the students to write a subtraction story problem that uses
sets and record the results in two ways. When they have completed this
task, encourage them to share their problem with a friend and add it to
their portfolios. You may wish to display the charts in the classroom.
In the example above, a set of 2 was taken away from a set of 6.