Skill: Add multiples of 10 mentally

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Adding a multiple of 10 to a whole number through 1,000 is understood as adding tens within the place-value system: the ones digit remains unchanged while the tens and, when needed, hundreds are recomposed (for example, 270 + 60 = 330). Mental reasoning may involve counting by tens or combining place-value units, including crossing a hundred; the focus is on whole-number sums in this range rather than larger-number generalizations or formal algorithms.

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Detailed Explanation: Add multiples of 10 mentally

When you add a multiple of $10$ , count by tens. The ones digit stays the same because you are adding tens, not ones.

Example: Find $270+60$ .

Think of $60$ as $6$ tens.
Count up $6$ tens from $270$ :

280,\ 290,\ 300,\ 310,\ 320,\ 330

The ones digit is still $0$ , and the tens have made a new hundred.

Therefore,

270+60=330.

You can also think of it as $27$ tens plus $6$ tens, which makes $33$ tens, or $330$ .

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Addition - Whole Number - Add Multiple of 10 to a Number

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