On the occasion if Deepawali festival, each student in a class sends greeting cards to other. If there are 20 students in the class, find the total number of greeting cards exchanged by the students?

Answer

`2 .^(20)C_(2)`

Explanation

Number of cards exchanged is `2xx` (number of ways 2 students can be selected who will exchange cards), which is given by `2 .^(20)C_(2)`.