how to find upper and lower limits of standard deviations from the mean
U = z SD + M. where, SD is the Standard Deviation and M is the Mean of the distribution. Thus, we get the corresponding value of the upper limit. We then find the lower limit L by making the sign of z score as negative and using the same formula again.L = z SD + M. First, we find out the various quantities we would need, like mean, standard deviation, variance, mid % amount of the distribution.n graph, the upper limit is shown as U and lower limit as L. We convert half of the % to decimal. In our example, we would get 0.25. Next, we check the Z-table for value we got as decimal number in the previous step. We write the closest value for the answer.