原帖由1楼楼主 nestor 于2008-06-17 20:30发表 Normal distribution, also know as the "bell-shaped curve". A population is the entire set of observations from which the sample, a subset, is drawn.
Your question is a Norminal question,
(Hints: 50% at + 0.67 sigma, 68.3% at + 1 sigma, 99.7% at +3 sigma, > 99.999999% at + 6 sigma.
.......