To round to 3 decimal places, look at the 4th decimal digit.<br><br>
&bull; 123.45678 &mdash; the 3rd decimal is 6, the 4th is 7.<br>
&bull; Since the 4th digit is 5 or more, round the 3rd digit up: 6 → 7.<br>
&bull; Drop all digits after the 3rd decimal.<br>
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Final Answer: 123.457