WAEC 2014 Mathematics · Question 4

If x = {0, 2, 4, 6}, y = {1, 2, 3, 4} and z = {1, 3} are subsets of u = {x:0 ≥\geq x ≥\geq 6}, find x ∩\cap (Y' ∪\cup Z)

Options

  1. A.{0, 2, 6}
  2. B.{1, 3}
  3. C.{0, 6)
  4. D.{9}

Answer: C. {0, 6)

Explanation written with AI and checked against the answer key

Analyze the question: We need X ∩ (Y' ∪ Z), where the universal set U is described as {x : 0 ≥ x ≥ 6}. This is almost certainly a typing error for 0 ≤ x ≤ 6, so U = {0, 1, 2, 3, 4, 5, 6} (integers).

Concept:

  • Y' (complement of Y) means the elements of U that are not in Y.
  • ∪ combines the elements of both sets.
  • ∩ picks only the elements common to both sets.

Solution:

  1. Y = {1, 2, 3, 4}, so Y' = U − Y = {0, 5, 6}.
  1. Y' ∪ Z = {0, 5, 6} ∪ {1, 3} = {0, 1, 3, 5, 6}.
  1. X ∩ (Y' ∪ Z) = {0, 2, 4, 6} ∩ {0, 1, 3, 5, 6} = {0, 6}.

Answer: {0, 6}, which is option C.

Note on the question: The universal set as written (0 ≥ x ≥ 6) is impossible, since no number is both at most 0 and at least 6. The intended meaning is 0 ≤ x ≤ 6, and that gives option C.

Tip: In set problems with complements, always write out the universal set first, then find the complement, then work through the brackets before the final intersection. Do it in the order: complement → union → intersection.

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