HOW TO ROUND OFF AN ANSWER TO A CALCULATION …

(The 5 is the first non-zero digit, so the 5 and both of the following digits are significant.) ... If the calculation involves both rules, though, you must keep track of the correct number of digits ... in each step. To avoid rounding errors in the final answer, keep track of the valid digits, but do not actually round off until your final answer. ................
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