What Bettser said.
Most high school problem sets advise you to answer to 2 decimal places (x.xx).
But to be more precise, look at the highest sig dig (aka sig figs) given in any # of the original problem. For instance, if a question throws out numbers like 2.34, 1.222, and 8.787777 in it, answer to 2 decimal places (2.34).
...and never use exponent "10^1" in scientific notation, because that's just "10". You'll likely get docked marks if you do, minimum in scientific notation is always "10^2", onwards.
---------- Post added at 05:28 PM ---------- Previous post was at 05:26 PM ----------
Are you following BEDMAS? Exponents first.
10^5 = 100,000
2.99 * 100,000 = 299,000
aka 2.99 * 10^5
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Never multiply your value by '10', then exponent it...remember BEDMAS.