Giả sử tỷ lệ bị bệnh X tại 1 thành phố là 9%. Khám ngẫu nhiên 81 người tại thành phố này, tính khả năng để có 27 người bị bệnh X.
Cần khám tối thiểu bao nhiêu người để khả năng gặp ít nhất 1 người bị bệnh X không ít hơn 9%?

  A: (3x−4)−(2x+2)=x−6

  B: The difference of the polynomials (3x−4) and (2x+2) is a polynomial, x−6, which shows closure under subtraction.

Step-by-step explanation:

Only two of the answer choices have anything to do with differences, and only one of those correctly computes the difference. That answer choice is the correct one in each case.

Often, these questions are mostly about choosing an answer that is responsive to the question. Answer choices in left-field can be ignored immediately.

When a set (polynomials) is closed under an operation (subtraction), it means that the result of that operation on any two members of the set is also a member of the set.

(Any sets containing 0 are not closed under division because division by 0 is undefined.)