According to the empirical rule, if the data form a "bell-shaped" normal distribution, approximately percent of the observations will be contained within 3 standard deviations around the mean.

According to the empirical rule, if the data form a "bell-shaped" normal distribution, approximately 99.7 percent of the observations will be contained within 3 standard deviations around the mean.  

To add, a bell curve is used to describe the mathematical concept called normal distribution, sometimes referred to as Gaussian distribution. 

During WWII, 120,000 Japanese-Americans were forced into camps, a government action that still haunts victims and their descendants. ... The roundups began quietly within 48 hours after the Japanese attacked Pearl Harbor, on December 7, 1941. The announced purpose was to protect the West Coast.

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