GATE | GATE-CS-2003 | Question 5

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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