The National Assessment of Educational Progress (NAEP) gave a test of basic arithmetic and the ability to apply it in everyday life to a sample of 840 men 21 to 25 years of age.Scores range from 0 to 500; for example, someone with a score of 325 can determine the price of a meal from a menu.The mean score for these 840 young men was x = 272.We want to estimate the mean score in the population of all young men.Consider the NAEP sample as an SRS from a Normal population with standard deviation = 60.

According to the 95 part of the 68-95-99.7 rule, 95% of all values of x with a sample size of 840 fall within ____ on either side of the unknown mean .What is the missing number?