Please help with these statistics questions. Thank you!

multiple choices

QUESTION 15 Which of the following statement(s) about degrees of freedom is/are correct: df = 4 in calculating between-group variation, when testing "whether five global manufacturing plants of Apple share the same monthly output" df = 4 in testing whether SAT scores follows N(66, 1002), i.e., a normal distribution with mean 660 and standard deviation 100; suppose the sample is grouped into 5 categories and large enough sample size. of = 10 in the distribution of Z, + Zz + ... + Z10, where Z1, ..., Z10 are independent standard normal random variables. O df = 100 in testing Ho: M = 100 against Hai M # 100 with a sample size of 100 and unknown population variance. O df = 34 in testing Ho: H1 - M2 2 25 against Hai M1 -M2