Chapter 3 - Probability - Exercises 3.1 - 3.34 - Learning the Mechanics - Page 120: 3.12e

$6$

Combinations Rule $$\binom{N}{n} = \dfrac{N!}{n! (N-n)!}$$ ${\displaystyle{\binom{6}{5}} = \dfrac{6!}{5! \, (6-5)!} = \dfrac{6!}{5! \, 1!} = \dfrac{6 \cdot 5 \cdot 4 \cdot 3 \cdot 2 \cdot 1}{(5 \cdot 4 \cdot 3 \cdot 2 \cdot 1)(1)}}$ ${\displaystyle{\binom{6}{5}} = \dfrac{6 \cdot 5 \cdot 4 \cdot 3 \cdot 2 \cdot 1}{(5 \cdot 4 \cdot 3 \cdot 2 \cdot 1)(1)}} = \boxed{6}$