n couples are invited to a party with the condition that every husband should be accompanied by his wife. However, a wife need not be accompanied by her husband. The number of different gatherings possible at the party is
(A) A
(B) B
(C) C
(D) D
Answer: (B)
Explanation: There are three options for every couple.
1) Nobody goes to gathering 2) Wife alone goes 2) Both go
Since there are n couples, total possible ways of gathering are 3n
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