The mean of a normal probability distribution is 400 the sta

Solution

If the data has a normal distribution, then approximately 68 percent of the data lies within one standard deviation of the mean. Therefore, for this particular problem, approximately 68 percent of the data lies between 400-12(1) and 400+12(1). In other words, about 68 percent of the data falls between the values 388 and 412

Similarly, approximately 95 percent of the data lies within two standard deviations of the mean. Therefore, about 95 percent of the data lies between 400-12(2) and 400+12(2), or between 376 and 424.

Finally, nearly all of the data lies within three standard deviations of the mean, which would be between 400-12(3) and 400+12(3), or the points 364 and 436