A small group of children. The material is arranged as for
addition. One child is in charge of the golden bead
material. One child is in charge of the large number cards and
another of the small number cards. The teacher thinks of a
problem, e.g. 3273 - 1528 - 487. She makes the minuend, 3273,
with the large number cards and the golden bead material, and places
them on the dark green mat. She makes the subtrahends, 1538 and
487, from the small number cards and places them in the upper right
hand corner of the felt lined trays. She gives a tray to each of
the children who will be doing the subtraction and asks them to read
their numerals. They do so.
The teacher, indicating the minuend, says to the children, "Here
is 3273. Tim is going to subtract 1538. How many units will
you
subtract, Tim?" Tim says, "Eight units." The teacher says,
"I do not have enough units. I only have three units. What
can we do?" She pauses and then explains that a ten bar equals 10
units. There are seven ten bars so one of them could be exchanged
for ten units. She gives a ten bar to one of the children.
He exchanges it at the bank for ten units. These are brought back
to the
teacher. She takes them and puts them above the golden beads on
the table. She says, "Now we have 10 units and 3 units, so we
have 13 units."
"Tim you can subtract 8." Tim does so.
Tim needs five hundred. There are only two hundred.
What can be
done? The teacher explains that a thousand equals 10 hundred, and
that
one of the thousands could be exchanged for ten hundred. One of
the
children takes a thousand to the banker
who gives 10 hundred squares in exchange. The teacher puts the 10
hundred squares above 2 hundred on the table. She says, "We have
ten
hundred and two hundred, so we have twelve hundred. Now Tim can
subtract 5 hundred." Tim does so. There are 7 hundred
left. There are 2
thousand on the table. Tim subtracts 1 thousand. There is 1
thousand
left.
The second child subtracts her subtrahend from the quantity
remaining on the mat. When necessary, one of a hierarchy is
exchanged
for ten of the next lower hierarchy.
As the subtraction is completed in each hierarchy, the number
remaining on the mat is counted, and the corresponding small number
card is placed beside it.
The teacher superimposes the small number cards. She places
them
under the large ones and re-caps. We had 3273. Tim
subtracted 1528.
Mary subtracted 487. So, the difference is 1248. More
problems are
worked in this way.
