1.7 Addition and subtraction: strategies within 10
Equip children with a range of useful strategies for addition within ten, including adding and subtracting zero and one, commutativity, adding and subtracting two to/from odd and even numbers, and doubling and halving.
- Teaching point 1: Addition is commutative: when the order of the addends is changed, the sum remains the same.
- Teaching point 2: Ten can be partitioned into pairs of numbers that sum to ten. Recall of these pairs of numbers supports calculation.
- Teaching point 3: Adding one gives one more; subtracting one gives one less.
- Teaching point 4: Consecutive numbers have a difference of one; we can use this to solve subtraction equations where the subtrahend is one less than the minuend.
- Teaching point 5: Adding two to an odd number gives the next odd number; adding two to an even number gives the next even number. Subtracting two from an odd number gives the previous odd number; subtracting two from an even number gives the previous even number.
- Teaching point 6: Consecutive odd / consecutive even numbers have a difference of two; we can use this to solve subtraction equations where the subtrahend is two less than the minuend.
- Teaching point 7: When zero is added to a number, the number remains unchanged; when zero is subtracted from a number, the number remains unchanged.
- Teaching point 8: Subtracting a number from itself gives a difference of zero.
- Teaching point 9: Doubling a whole number always gives an even number and can be used to add two equal addends; halving is the inverse of doubling and can be used to subtract a number from its double. Memorised doubles/halves can be used to calculate near-doubles/halves.
- Teaching point 10: Addition and subtraction facts for the pairs five and three, and six and three, can be related to known facts and strategies.