Question

There are 130 people at a meeting. Theyeach give a Valentine's Day card toeveryone else. How many cards weregiven?

Answer 1

Permutations

Suppose there are only two people in the meeting. Person A gives a card to person B and vice-versa. Two cards were given.

Now we have 3 people. Person A gives two cards. Person B gives two cards. Person C gives two cards. Total = 6 cards given.

Each people gives a card to everyone else (except themselves, of course) and it's done by everyone in the meeting, thus for 130 people:

130 x 129 = 16,770 cards were given