Adding a multiple of 10 to a two-digit number is understood as increasing the tens value while keeping the ones value unchanged; for example, 47 + 30 is 7 ones and 7 tens, or 77. The reasoning relies on place value and composing or decomposing groups of ten, and applies to sums within 100 rather than to larger numbers, formal multi-digit algorithms, or generalized symbolic rules.
When you add a multiple of 10, the ones digit stays the same. You only increase the number of tens.
Example: Find .
So, is tens and ones:
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