## Thinking Mathematically (6th Edition)

The number of possible combinations if r items are taken from n items is nCr = $\frac{n!}{r!(n-r)!}$ 6C0 = $\frac{6!}{0!(6 -0)!}$ =$\frac{6!}{0!6!}$ 0!=1, so the expression reduces to 1.