Definition
Near-doubles strategy
The near-doubles strategy uses a known double and adjusts by the small difference between the addends.
What it means
When two addends are almost the same, start with the double you know. Then move one step up or down to match the original pair. The adjustment must equal the change you made.
Remember it
Almost a double: double first, then fix the tiny difference.
Example
For 8 + 9, use 8 + 8 = 16, then add the extra 1 from the 9. So 8 + 9 = 17.
Watch for
It works best when the addends are close; it is not a rule that every sum must use a double.
Common mix-up
If you change 9 to 8, add the removed 1 back; otherwise the sum changes.
Exact meaning
For two addends that differ by a small amount, the near-doubles strategy replaces one addend to form a known double, then compensates by the same amount.