NEGATIVE STRIP BOARD
Memorization of the subtraction combinations.
The Negative Strip Board is a replica of the Addition Strip Board in size and number of squares.
The only differences are that a blue line divides the board vertically after the ninth square, the first 9 numerals are blue and the numerals from 10 to 18 are in red.
Two sets of colored strips, one set in red and the second set in blue.
A third set of plain wooden strips, not numbered.
There are seventeen of these ranging from one square in length to seventeen squares.
Squared paper and pencil.
Subtraction Control Chart #1.
At a table, examine the board.
Note the blue line. Introduce the wooden strips and build a stair with them.
The wooden strips are placed vertically above the board from longest to shortest respectively placed above the numerals 1 to 17.
The child builds the blue stair to the right of the board.
Note: To take away, always begin with the largest blue strip, never record an answer in red.
Point to the 18 on the board and ask the child to identify it.
State that the blue strips are used to take away.
They represent the subtrahend.
Place the 9 blue strip on the board.
Align it on the right, beginning with the number 18 representing the minuend and cover up the numerals along the top of the board with the plain wooden strip.
The answer is found directly to the left of the blue strip.
Write the equation, 18 – 9 = 9.
Repeat using the next strip in diminishing order.
The answer is in red, therefore, the child will not write down the equation.
Move across the numerals on the board, from right to left, to locate the next minuend, ie. 17.
We no longer need 18.
Cover the numeral(s) with the appropriate wooden strip directly above the current minuend, ie. 17.
Proceed as above.
When the child reaches 9 as the minuend he may need some help as he will get zero for an answer, 9 – 9 = 0.
When 8 is the minuend, tell the child not to record an answer where the blue strip goes beyond the left barrier of the grid.
The child checks his work with the Subtraction Control Chart #1.
Exercise: As in the presentation, the child works through all the tables.
Set out the materials as before.
The child sets out the red strips in stair formation to the left of the board.
The child chooses a number, ie. 6 or 7.
Using the wooden strip cover the extra numerals to the right of the minuend.
The child writes the minuend centerd at the top of the page and builds a table.
Beginning with the red strips build a table as in the Addition Strip Board Exercise 2a beginning with the largest addend.
The last row will be the minuend represented by one blue strip.
This is only possible for minuends less than 10. “Now we’re going to take away the blue strips.”
Using the board, note the minuend, ie. 6.
The child writes ‘6’. Take away the first blue strip, ie. 6, sliding it to the bottom right of the board.
‘What’s left? – Nothing.’
The child finishes the equation, ie. 6 – 6 = 0.
Note: the difference is indicated by the red strip or its absence.
Proceed in the same manner, working up through the rows.
Check the work with Subtraction Control Chart #1.
Subtraction Control Chart #1.
5.5 – 6.5 years