analytical chemistry standard deviation [closed]

Analysis of a bottle of $100$mg of vitamin C, yields an average vitamin content of $99.8\pm0.3$ mg. Assuming Gaussian statistics, which of the following is true and the answer is $68\%$ of tablets contains between $99.5$ and $100.1$ mg of vitamin C how is that?

closed as off-topic by Klaus-Dieter Warzecha, Michael DM Dryden, Todd Minehardt, airhuff, bonMar 12 '17 at 10:07

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