\# \text{Pillar sets} = \begin{pmatrix} 5 \\ 3 \end{pmatrix} = \frac{5!}{3! \cdot (5-3)!} = \frac{4 \cdot 5}{1 \cdot 2} = 10, \ \ \ \ \ P(\text{Best pillars}) = \frac{1}{10} = 10\%