Answer:
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Using the formula for the union of two sets:
- |A ∪ B| = |A| + |B| - |A ∩ B|
where
- |A| represents the number of elements in set A,
- |B| represents the number of elements in set B, and
- |A ∩ B| represents the number of elements in both sets A and B.
We are given that:
- |A| = 39
- |A ∩ B| = 1
- |A ∪ B| = 80
Plugging in the values, we get:
- 80 = 39 + |B| - 1
- |B| = 80 - 38
- |B| = 42
Therefore, set B contains 42 elements.