A new plant manager claims that he will be able to reduce safety violations. The average number of weekly violations over the last 5 years was 10. We don't know how much variation there is in that known population. After the new plant manager starts, safety violations are measured during a sample period of 4 weeks and the average is calculated. Which test will be used to determine whether the sample average is different from the previous 5 years' average? [ Choose ] one sample t test , z test, independent sample t-test, repeated measure t test