Empirical rule can be used to estimate the number of values that lie with 1, 2 or 3 standard deviations of a Normally distributed population.
According to the empirical rule, 95% of the values lie within 2 standard deviations of the mean.
Total number of bulbs = n = 560
95% of n = 0.95 x 560 = 532
This means, 532 bulbs will lie within 2 standard deviations from the mean
