A) \[^{20}{{C}_{2}}\]
B) \[2\ .{{\ }^{20}}{{C}_{2}}\]
C) \[2\ .{{\ }^{20}}{{P}_{2}}\]
D) None of these
Correct Answer: B
Solution :
\[2\ .{{\ }^{20}}{{C}_{2}}\] {Since two students can exchange cards each other in two ways}.
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