The fastest way to go about this is to simply determine what each point really says and if its possible to have different solutions.
For one this is definitely the case, because we can have 20 students own a car or we can have 30, we have no idea, so it is insufficient.
Two is a little bit more tricky, let's look at what it is actually saying here: of the students who own a car 42% must be female. We have to remember that, because it is people, they have to be whole numbers. 42% is equal to 21/50, which cannot be simplified any more, so we know that the number of students who own a car must be a multiple of 50. The only multiple of fifty that works with the constraint that there must be 80 people is 50 itself, therefore we know that this is sufficient.
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Eliza
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