Combinatorics

The city has 7 fountains. Works only 6. How many options are there that can squirt ?

Correct result:

n =  7

Solution:

$$\begin{gathered} C_6(7)=\left({\displaystyle \genfrac{}{}{0px}{}{7}{6}}\right)={\displaystyle \frac{7!}{6!(7-6)!}}={\displaystyle \frac{7}{1}}=7 \\ n=\left(\genfrac{}{}{0px}{}{6}{7}\right)=7 \end{gathered}$$

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