There are three catergories of problem structures for addition and subtraction situations. They are the part-whole concept, comparison concept and change concept. Drawing models while doing problem sums help children to see the relationship between the three numbers in the sums clearly.
While doing addition and subtraction, there are also different properties to guide us. The commutative property of addition states that we can change the order of the addends of an addition sum and it does not change the answer. The associative property of addition shares that when adding three or more numbers, it does not matter which pair of addens is added first, the answer is still the same. Using zero are good methods of helping children understand zero as an identity element in addition and subtraction. This concept of zero property will help children become more flexible in how they combine numbers.
Although the preschoolers I teach need not learn how to solve problem sums formally, I have an important role to play in their learning of mathemtics. My role now is to help the children develop their number sense and let them see the relationships between numnbers 1 through 10.