One large course has 900 students, broken down in section meetings with 30 students each. The section meetings are led by TA's. On the final, the class avg is 63 and the SD is 20. However, in one section the avg. is only 55. The TA argues this way:
If you took 30 students at random from the class, there is a good chance they would avg below 55 on the final. Chance variation.
Is this a good argument? Yes or no, explain.