Exam-style question
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Let A = {1, 2, 3, 4} and B = {3, 4, 5}. Determine A ∪ B, A ∩ B and A\B. State the meaning of each operation.
Model answer
What a good answer should say
- A ∪ B = {1, 2, 3, 4, 5}; A ∩ B = {3, 4}; A\B = {1, 2}.
- The union contains every element that is in A or B.
- The intersection contains elements that are in both A and B.
- The difference A\B contains elements that are in A but not in B.
Explanation
Why this works
For the union, repeated values are included only once because a set contains each value at most once. The common elements are 3 and 4, giving the intersection.
Removing the elements of B from A leaves 1 and 2.
Common mistake
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