This understanding involves decomposing each two-digit addend, from 10 to 99, into tens and ones and combining corresponding place-value units when the ones sum and tens sum are each 9 or less. The learner connects the written column method with expanded form or place-value representations, preserving the value of each digit and recognizing that no unit is exchanged for a higher place; additions requiring regrouping, larger numbers, or more general multi-digit procedures are outside this scope.
To add two 2-digit numbers without regrouping:
Example: Add .
Write the numbers in columns:
34
+ 25
----
Add the ones: .
Add the tens: tens tens tens.
So,
34
+ 25
----
59
Using expanded form:
Combine tens and ones:
Then add:
So, .
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