This understanding involves decomposing each two-digit addend into tens and ones, combining tens with tens and ones with ones, and then joining the partial sums when the ones sum is less than ten and the total remains below 100. Place-value drawings, expanded notation, and open number lines can show why the result is unchanged by adding like units; regrouping a ten, the standard algorithm, and larger or more general numbers are not included.
Break each number into tens and ones. Add the tens together, then add the ones together. Finally, combine those two sums.
Example: Find .
So,
The ones sum is , which is less than , so no regrouping is needed.
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