Learning Resources Base Ten Set Aktivitätsanleitung Seite 3
Addition
Have students build the following to reinforce three-digit addition with regrouping:
Build 276 (2 flats, 7 rods, 6 units)
Build 835 (8 flats, 3 rods, 5 units)
Combine first the units, then the rods, and then the flats:
10 flats
Exchange smaller pieces for larger pieces whenever possible:
1 cube
Record:
Th
+
1
Subtraction
Example A:
Top row:
3 cubes 4 flats 8 rods 7 units
Second row: 1 cube 2 flats 6 rods 4 units
Ask a student to take away from the top row
as many as he or she sees in the second row.
This second row should not be touched,
only viewed. Such a rule will become more
important as you solve problems involving
regrouping.
Subtraction with regrouping should only
be handled by children who have grown
familiar with the equivalences among the
pieces.
Example B:
Top row:
3 cubes 2 flats 2 rods 3 units
Second row: 1 cube 7 flats 6 rods 9 units
Ask a student to take away from the top row
as many as he or she sees in the second row.
Remind the student that the second row
should not be touched.
Encourage students to follow these
regrouping steps:
1. You cannot take 9 units from 3, so
exchange 1 rod for 10 more units. Then,
take 9 units, leaving 4.
2. You now have 1 rod. But you cannot take
1 flat
H
T
O
2
7
6
8
3
5
1
1
1
10 rods
1 rod
away 6 rods from 1 rod, so exchange 1
flat for 10 rods. Now, take 6 rods from 11
rods, leaving 5 rods.
3. You cannot take 7 flats from 1 flat, so
exchange 1 cube for 10 flats. Then, take
away 7 flats from this pile of 11 flats,
leaving 4 flats.
4. Finally, take 1 cube from the 2 cubes,
leaving 1 cube.
To record, a child might write:
Top row:
Second row:
Remainder in
top row:
It is often helpful for students to view
subtraction as the inverse of addition.
Adding pieces to one row to match a first
row can provide experience in regrouping.
Example C:
Top row:
3 cubes
Second row: 1 cube 8 flats 9 rods 7 units
Ask students, "How much larger is the top
row than the second row? That is, how
much must you add to the second row to
get to the top row?"
By thinking of this problem in terms of
adding to the second row, students will take
the following steps:
1. Three more units will give 1 more rod.
(3 units)
11 units
1 unit
Th
H
T
O
3
0
0
0
1
8
9
7
1
1
0
3
