Understanding subtraction

The purpose of this activity is to ensure that children focus first on the number from which a lesser number is to be subtracted - the starting number being the first to be given attention.

Concrete objects are used to demonstrate the principle of a starting numbr. Subtraction is demonstrated by removing some of those objects.

Example: Subtraction from 7

Step 1
Teacher hides all 7 items under her hand or under a cover and asks: How many are under there?
Have I enough to be able to take 3 away?

Teacher then removes 3 items leaving the remainder hidden.
How many will be left?
Check.

Step 2
Teacher gives each child a set of counters (9) and asks that 7 be selected and put in a line.

Each child is given a strip of card or thick paper long enough to cover the items, and asked to write the number of items on the left side of the paper (i.e., 7).

Teacher says, "Cover the counters with your card. How many counters are there? Do you have enough to be able to take 4 away?"

Slide your card sideways till you uncover 4. Take them away.
"How many do you think are left under the card?"
Three. Check. Are there three?
Let's write down on your card what you have done. 7 - 4 = 3"

Margaret Toohey