This is a strategy that I think a lot of people use, without realizing that they do it.
In this strategy you look for compatible numbers, or two numbers that you can add, together to reach a ten.
For example:
17 + 379 + 13=
the 7 and the 3 are compatible and add to make an additional 10 turning the problem into
10 + 379 + 10 + 10=
or
379 + 30 = 409
Another example:
42 + 612 + 18 =
the 2 in 42 and the 8 in 18 are compatible, making
40 + 10 + 10 + 612 = 60 + 612 = 672
Or another way to do it is using the left to right method:
12 + 16
break out your addends to their place values:
(10+10) + (2+6)
finish adding
20 + 8 = 28
another example
25 + 23
(20 + 20) + (5 + 3)
40 + 8
48
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