Class 11MathematicsPermutation and CombinationDefinition of permutation, Number of permutations with or without repetition, Conditional permutations
EasyOn the occasion of the Deepawali festival,each student of a class sends greeting cards to every other student. 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$2 \times ^{20}C_2$
- C$^{20}P_2$
- DNone of these
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