The two little girls are working out problems in seven figures. (The Washington Montessori School, Washington, D. C.)
SUBTRACTION
The counting-frame lends itself equally well to problems in subtraction. Let us take, for example, the following:
8947-
6735
=
We place the beads representing the first number; then from them we take the beads representing the second number The beads remaining indicate the difference between the two numbers; and this is written: 2212.
Then comes the more complicated problem where it is necessary to borrow from a higher denomination. When the beads of one wire are exhausted, we move over the entire ten and take to represent them one bead from the lower wire; then we continue the subtraction. For example:
8954-
7593
=
We move the beads representing the first number; then we take 3 beads from the units. Now we begin to subtract the tens. We wish to take away 9 beads; but when we have moved five the wire is empty, and there are still four more to be moved. We take away one bead from the hundreds-wire and replace the entire ten on the tens-wire; and then we continue to move beads on the tens-wire until we have taken a total of nine—that is, we now move the other four. On the hundreds-wire there remain but 8 beads, and from them we take the 5, etc. Our final remainder is 1361.