# Examination

The class is 21 students. How many ways can choose two to examination?

n =  210

### Step-by-step explanation:

$n={C}_{2}\left(21\right)=\left(\genfrac{}{}{0px}{}{21}{2}\right)=\frac{21!}{2!\left(21-2\right)!}=\frac{21\cdot 20}{2\cdot 1}=210$

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