Model = Binomial 
  Formula = Probability

\[ \begin{align} P(X=k) &= &^nC_r &\cdot &(p)^{k} &\cdot &(1-p)^{n-k} \\ \end{align} \]

\[ \begin{align} P(X=k) &= &^nC_r &\cdot &(p)^{k} &\cdot &(1-p)^{n-k} \\ P(X=k) &= &\begin{align} \text{Positions} \end{align} &\cdot &(p)^{k} &\cdot &(1-p)^{n-k} \\ \end{align} \]