Relating Addition and Subtraction

As adults we know that every addition result gives two results in subtraction. For example,

The question "7 and what makes 12?" and "7 from 12 leaves what?" are identical questions.

Some children know that "7 from 12 leaves 5," not because any subtraction has been carried out but because they know that "7 and 5 are 12." However, it is wrong to assume that all children would get these relations automatically. There is always a special need to bring to children's notice the relationship between the addition and subtraction facts.

I have found it always beneficial to give children experience in linking subtraction facts with addition facts. This is because a child's memory of both addition and subtraction facts is helped if the child understands that each subtraction fact is related to an addition fact that they have already learned separately. For example, if a child knows that 9 + 8 = 17 and 8 + 9 = 17, he or she easily learns that 17 - 9 = 8 and 17 - 8 = 9.

I have found the following two ways for providing experience in teaching the relation between addition and subtraction facts very useful and interesting.

1. A practice card for subtraction and addition check A sample of this type of practice cards is shown in the figure below.

These could be prepared by using the backside of old greeting cards or light cardboard. The practice card in the figure above gives experience in dealing with some related facts. The front of the card gives subtraction facts. The back of the card gives related addition facts, which serve the purpose of checking the subtraction.

A convenient way of using this card is to attach to the right side of the card a slip of paper on which the child writes his answers after putting his name on the back. In the figure above this portion is indicated in blue. This way the same card can be reused on another occasion. Children can write their own answers if it is pointed out to them that the first figures on the left-hand side of the addition part of the card are the answers to the examples on the subtraction part of the card (and vice versa). Children find this activity very interesting. More such cards should be prepared to cover all the basic facts discussed in the articles Speedy and Accurate Addition(part I) and Dealing with Subtraction (I)

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