 This Math video lesson is designed for 6-12-year-old children to help them practice subtraction using the Montessori Subtraction strip board.

## What is the Subtraction Strip Board?

The Montessori Subtraction Strip Board has two parts: a board and strips.

• The board is divided into squares (each 2cm x 2cm) across from left to right and 11 squares from top to bottom. The topmost squares are numbered 1 to 18; from 1 to 9 in blue and from 10 to 18 in red. The board is divided vertically by a blue line after the number 9.
• The strip box of the strip board consists of two sets of strips, namely red and blue. Each set of strips has numbers written from 1 to 9. The red strips are further divided into small squares with blue lines. The end square of each strip is marked with the symbol that corresponds to the number of its squares.
• In a set of plain wooden strips (not colored or numbered), the first and smallest strip (2 cm x 2 cm) is added one square to its length with each succession strip, so that the last strip is 17 squares long.
• There is a subtraction chart also that helps the child to tell the child all the combinations of subtraction. It is also used as a control card. The Subtraction strip board is introduced after the child is well-versed with the addition strip board to help them learn the concept of subtraction.

## The Purpose of Introducing the Subtraction Strip Board to the child

Montessori Subtraction strip board teaches children the mathematical concept of subtracting numerals 1 to 18 more abstractly as it leads the child through all the combinations in subtraction.

The subtraction board contains a blue line between 9 and 10, showing that the units beyond the 10 need to first be removed before the subtraction can be made within the 10. For example, when we add 12-5, the blue line shows how many points went below 10 and how many points needed to be subtracted extra.

## Control of Error

As the child counts using blue and red strips, the difference does not go beyond 9-9.

## How to Introduce the Subtraction Strip Board to the child?

1. Invite the child to the table along with the subtraction strip board.
2. Tell them, “Today, we will learn how to subtract numbers or Subtraction.”
3. Introduce the child to the Subtraction strip board. Show the child boxes, the number at the top of the board, and the blue line on the board, which shows us we have reached the difference of nine.
4. Tell the child this strip board will help us find the difference between numerals 1 to 18.
5. Show the child the strips you will use for subtraction.
6. Have the child take out all the blue strips one by one and read the numbers written on them.
7. Have the child place them in order to the left of the chart.
8. Now, ask the child to take out the red strips and place them in order to the right of the board, as shown in the video.
9. Have the child place the wooden sticks on top of the numerals written on the board.
10. Tell the child that we must first choose a minuend, such as 9
11. Cover up the numbers 10-18, starting with 18 using the blank strips as we don’t need them.
12. Now let’s say, we need to take 4 from 9.
13. Have the child choose one blue strip (let’s say, numeral 4) and place it directly to the left of the blank strip.
14. Read, 9 minus 4 is 5” Point to the 5 directly to the left of the blue strip.
15. Using red strips, ask the child to place them after the blue strips, as shown in the video.
16. Show the child how to check the result by pointing it out on the control chart.
18. Have the child replace the blue strips and repeat finding the difference between numerals 1 to 18.
19. Encourage the child to do all the tables.

The Subtraction strip board material explained in the videos allows the child to practice the operations of subtraction with different sequences on the subtraction strip board, as shown in the video.

Watch the video and learn the difference between the numerals in a fun and innovative way to instill a sense of logical thinking in the child. It helps the child to get a better understanding of complex math concepts.