His mistake was that he did not use a random sample. His tried to show that playing games would give him higher grades which his study does not decisively conclude because the people around him that play games are likely to be in the same academic caste as him, which skews his data. Choice B would be the best because he's not testing any variables, rather just collecting the unadultered data of the group.
Answer:
35
Step-by-step explanation:
160-125
