First it selects all the female students. Next it takes the studids of all the female students present. Then it cross with all the courseid s present, which creates extra records which are the tuples where some female students not enrolled for some courses. When we set difference the two sets, the extra records that is the tuples, in which, course IDs are presentwhich are not enrolled by some-some females. Here is the catch - if some course is not enrolled by some female, it may have been enrolled by some other female as it is mentioned in the question [...]

There's a clear statement saying that "J might contain other elements than that of the elements in the given set"  ,So , try to derive other elements and do not confuse that there will only be three elements in the set JAnswer: C;-> J has to contain 0, as 0 is identity element for the main group , other than 0 , we have those 3 exact elements from set (at least) , and (at most)  we can have many other elements in J. [...]

B [...]

9 [...]

Given information: - Dick is thrice as old as Tom. Let Tom's age be x. - Harry is twice as old as Dick. - Dick's age is 1 year less than the average age of all three. Step 1: Express Dick's age in terms of Tom's age (x). Dick's age = 3x Step 2: Express Harry's age in terms of Dick's age. Harry's age = 2 × Dick's age = 2 × 3x = 6x Step 3: Set up an equation for Dick's age being 1 year less than the average age of all three. Dick's age = (Tom's age [...]