\((_{k}^{n})= \textrm {num of ways to pick k from n}\) 4 employees, team of 2 \(7*6*5/6\)

\(\((_{k}^{n})=C(n,k)=_nC_k=\frac{n!}{(n-k)!k!}\)\)¶

The number of subsets of a set of size \(n\) each with cardinatily \(k\)

\(\(P(n,k)=_nP_k=\frac{n!}{(n-k)!}\)\)¶

\(\(|\mathcal{P}(A)|=2^n\)\)¶

Where \(n\) is the number of elements in \(A\)

\(A.B.C.D.E\)¶

\(\(5*4=\frac{5!}{(5-2)!}=\frac{5*4*3!}{3!}=5*4\)\)¶

6 students in row 1 arrange 3 \(P(6,3)\) or (Choose 3 from 6)*(order the 3 we picked) \(P(6,3)=\frac{6!}{(6-3)!}\) \(\frac{6!}{(6-3)!}3!\)

n students in row 1 arrange k \(P(n,k)\) or (Choose k from n)*(order the k we picked) \(P^n_k=\frac{n!}{(n-k)!}\) \(\frac{n!}{(n-k)!k!}\)