In a colony, there are 55 members. Every member posts a greeting card to all the members. How many greeting cards were posted by them?
Answer: C
First player can post greeting cards to the remaining 54 players in 54 ways. Second player can post greeting card to the 54 players. Similarly, it happens with the rest of the players. The total numbers of greeting cards posted are
54 + 54 + 54 …
54 (55times) = 54 x 55 = 2970.