On the occasion of Deepawali festival each student of a class sends greeting cards to the others. If there are $20$ students in the class, then the total number of greeting cards exchanged by the students is
On the occasion of Deepawali festival each student of a class sends greeting cards to the others. If there are $20$ students in the class, then the total number of greeting cards exchanged by the students is
- A
$^{20}{C_2}$
- B
$2\;.{\;^{20}}{C_2}$
- C
$2\;.{\;^{20}}{P_2}$
- D
None of these
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- [IIT 1994]
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