Re: % within x SDs of mean question
in a standard normal distribution with a mean of zero,
1 SD: .3413 or +/- 1 SD: .6426
2 SD: .4772 or +/- 2 SD: .9544
3 SD: .4987 or +/- 3 SD: .9974
As an additional note, that's why Six Sigma is so common in business applications, because it represents 99.74% of the distribution...
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