Help with STATS homework

Scores for men on the verbal portion of the SAT-1 test are normally distributed with a mean of 509 and a standard deviation of 112 (based on data from the College Board). Randomly selected men are given the Columbia Review Course before taking the SAT test. If one of the men students is randomly selected, find the probability that his score is at least 540. Assume the course had no effect. Round to the nearest thousandth. (i have this part answered but the information is needed for the next question) > If 16 of the men are randomly selected, find the probability that their mean score is at least 540. Again, assume the course had no effect. Round the probability to the nearest thousandth. why can the central limit theorem be used even through the sample size does not exceed 30? (Points : 1)