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Subsets of an $n$-element Set

COMBIN-WOVGOV

Which two expressions count the number of subsets of an $n$-element set?

Select ALL that apply.

A

$\sum_{k=0}^n{n\choose 2}$

B

$\sum_{k=0}^n{n\choose k}$

C

$\sum_{k=0}^n 2^k$

D

${n\choose 2}$

E

$2^n$

F

$n^2$