Question

The manager of a night club in boston stated that 95% of the customers are between the ages of 21 and 27 years. if the age of customers is normally distributed with a mean of 24 years, calculate its standard deviation.

Answer 1

95% of a normal distribution lies within ±1.96 standard deviations of the mean. That is, ±3 years represents ±1.96 standard deviations, so ...
.. the standard deviation is 3/1.96 = 1.53 years.