You may have already learned different forms in which a number can be written. "Expanded form" is a form in which the digits are summed according to their place value:
35 = 30 + 5, for example, or
459 = 400 + 50 + 9
The "make a ten" strategy for addition or subtraction makes use of this different form of number representation. Also, it makes use of some additional facts, based on subtraction, rather than addition.
9 = 10 - 1
8 = 10 - 2
7 = 10 - 3
and so on.
Generally, the strategy is to represent a number in terms of a convenient multiple of 10, then perform the addition and/or subtraction.
Example 1
34 + 23 = (30 + 4) + (20 + 3)
= (30 + 20) + (4 + 3)
= 50 + 7 = 57
Example 2
34 + 28 = (30 + 4) + (30 - 2)
= (30 + 30) + (4 - 2)
= 60 + 2 = 62
Example 3
34 - 28 = (30 + 4) - (30 - 2)
= (30 - 30) + 4 -(-2)
= 4+2 = 6
The break apart strategy is similar, except you are not constrained to choose multiples of 10.
Example 4
34 - 28 = (38 - 4) - 28
= 10 - 4 = 6
Here is another discussion of break apart strategy.
35 = 30 + 5, for example, or
459 = 400 + 50 + 9
The "make a ten" strategy for addition or subtraction makes use of this different form of number representation. Also, it makes use of some additional facts, based on subtraction, rather than addition.
9 = 10 - 1
8 = 10 - 2
7 = 10 - 3
and so on.
Generally, the strategy is to represent a number in terms of a convenient multiple of 10, then perform the addition and/or subtraction.
Example 1
34 + 23 = (30 + 4) + (20 + 3)
= (30 + 20) + (4 + 3)
= 50 + 7 = 57
Example 2
34 + 28 = (30 + 4) + (30 - 2)
= (30 + 30) + (4 - 2)
= 60 + 2 = 62
Example 3
34 - 28 = (30 + 4) - (30 - 2)
= (30 - 30) + 4 -(-2)
= 4+2 = 6
The break apart strategy is similar, except you are not constrained to choose multiples of 10.
Example 4
34 - 28 = (38 - 4) - 28
= 10 - 4 = 6
Here is another discussion of break apart strategy.
