I think the answer to question No.1 should be B because between 20 and 24 only 20 can meet the requirements that all the three numbers are divisible by 5. So 2) alone is enough.
Meanwhile, anyone has the answer to question No.3? I just have no idea about it.
set X has 5 numbers, and the average is greater than medium; set Y has 7 numbers, and the average is greater than medium. set Z combined x and y, is the average greater than medium?
(1) medium of set X is greater than medium of set Y (2)average of set X is greater than average of set Y