2 Develop the Concept: Interactive
10–15 min
Overview
Interactive Learning
In this activity, children will model subtracting a one-digit number from a
two-digit number and record their work.
Essential
Question
When subtracting, how do you know when you need to regroup?
Materials
Place-Value Mat A enlarged to 11 ⫻ 17 (Teaching Tool 7, 1 per child),
connecting cubes (30 per child), number cube labeled 4–9
Set the Purpose You have learned that when subtracting, you sometimes
have to regroup 1 ten as 10 ones. Today you will learn how to record the
subtraction.
Connect Remind children that in the last lesson they learned how to
regroup. How did you regroup in the last lesson? [I made 10 ones from
1 ten.] Was the number of connecting cubes on your mat the same after
you regrouped as before? [Yes]
There are 22 children drawing a picture. 4 of them finish drawing. How
many children are still drawing? Encourage children to share their ideas
on how to solve the problem. If no one suggests it, guide children to
model the story using connecting cubes.
Name ____
Whole-Class
Participation
Work on page 255 with cubes and mats. Invite a child to choose
a number from 20–23. How many tens do you have? How many
ones? [Have children write answers in the subtraction frame in
Item 2.] Another child tosses the number cube for a one-digit
subtrahend. Do you need to regroup in order to subtract? Circle
Yes or No. Guide children to regroup the cubes if necessary and then
complete the subtraction. Repeat this activity for Item 3.
Restate the first problem as: There are 22
children drawing a picture. 4 more children join
them. How many children are now drawing?
What operation would you use to solve this
problem? [Addition. You added because more
children joined. 26 children are now drawing.]
________
__
IZch
Lesson
9-2
Education,
Inc.
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Sample an
swers
provided
below.
© Pearson
On the board, draw a two-digit subtraction frame. Solve the problem
using connecting cubes and record the steps. Have children model h
22 with cubes on their Place-Value Mats. As you write on the board,
encourage children to make the connection between the cubes on
the mat and the subtraction frame in Item 1. How many tens are in
22? [2] How many ones? [2] What number are you subtracting from
22? [4] Do you have enough ones to subtract 4? [No] How can you
subtract, then? [Regroup] Children circle Yes in Item 1, explain how
to regroup, and do so with their cubes. How many tens do you
have now? [1] How many ones? [12] Do you have enough ones to
subtract now? [Yes] Children model subtracting the ones, then the
tens. Show children how to record the difference. [18]
FOLD
Model/
Demonstrate
________
________
________
M o d e ls to
___
S u b tr a c t
Twoand OneD ig it N u m
b e rs
FOLD
Pose the
Problem
IZch
1.
DcZh
1
12
2
2
IZch
2.
1
8
Yes
No
IZch
3.
2
4
Regroup?
DcZh
1
3
2
3
2
0
Regroup?
Yes
No
DcZh
10
0
6
1
4
Regroup?
Home Con
nec
two-digit num tion Your child use
d connecting
ber, with
Home Act
cubes to mo
ivity Write and without regrou
del subtrac
pin
22
22 – 6 usin
ting a
g small obj – 6 in vertical form g. Then your child
recorded the one-digit number
on a piece
ects such
Understand
from a
as
of
subtraction
paper clip
s, buttons, paper. Ask your chil
.
from a two It! Models can be
d to
or pennies.
used to sho
-digit num
Have your show you how to sub
ber.
w if regrou
child write
ping is nee
Topic 9 •
the differe tract
ded when
Lesson 2
nce.
subtracting
a one-digit
number
Yes
two hundred
No
fifty-five
255
Link to Investigations,
Second Edition
Joint-Usage Master Plan
Blended Instruction (Plan 1):
Topic 9 and Unit 6
Models to Subtract Two- and One-Digit Numbers 255
28264_255a-258b_PDF.indd 255
6/19/07 10:10:14 AM