About 68 % of the data falls within 1 standard deviation from the mean.
About 95 % of the data falls within 2 standard deviation from the mean.
About About 99.7 % of the data falls within 3 standard deviation from the mean.
Further more, since the graph is symmetric we can divide the arc into eight parts, and know what percentage of the graph is contained in each part.
We can use these properties and known percentages to find percents of data and probabilities of events for problems following this type of distribution. We just have to find how many standard deviations from the mean the data value of interest is, then we can compare it directly with the normal curve.
