The classroom mean score is 96, which is −2.47 standard error units from the population mean of 100. Looking up the "z"-score in a table of the standard normal distribution cumulative probability, we find that the probability of observing a standard normal value below −2.47 is approximately 0.5 − 0.4932 = 0.0068. This is the one-sided "p"-value for the null hypothesis that the 55 students are comparable to a simple random sample from the population of all test-takers. The two-sided "p"-value is approximately 0.014 (twice the one-sided "p"-value).