A sample mean and a stated normal interval

For a mathematical survey-analysis exercise, a simple random sample of one hundred independent observations has mean monthly expenditure of five hundred thousand won. The population standard deviation is supplied as one hundred thousand won, and the exercise directs use of a normal critical value of 1.96 for a ninety-five percent interval. Sampling is assumed sufficiently small relative to the population that finite-population correction can be ignored. A colleague divides the population standard deviation by one hundred instead of its square root. Another describes the resulting interval as containing ninety-five percent of individual expenditures. The task is to calculate the interval under the supplied assumptions and distinguish the population mean from individual observations.