Question
Evaluate: $\frac{n !}{r !(n-r) !}$ for

n = 8, r = 6

Answer

$n =8, r =6$

$\begin{aligned} \therefore \quad \frac{n !}{r !(n-r) !} & =\frac{8 !}{6 !(8-6) !}=\frac{8 \times 7 \times 6 !}{6 ! 2 !} \\ & =\frac{8 \times 7}{2 !}=\frac{8 \times 7}{1 \times 2}=28\end{aligned}$

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