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30C5

 Oct 5, 2016
 #1
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30C5 =30! / (30-5)!. 5! =142,506

 Oct 5, 2016
 #2
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30C5

 

\(\begin{array}{|rcll|} \hline && 30C5 \\ &=& \binom{30}{5} \\\\ &=& \dfrac{30!}{(30-5)!\cdot 5! } \\\\ &=& \dfrac{30!}{ 25! \cdot 5! } \\\\ &=& \dfrac{25!\cdot 26 \cdot27 \cdot 28 \cdot 29 \cdot 30}{25!\cdot 5! } \\\\ &=& \dfrac{ 26 \cdot27 \cdot 28 \cdot 29 \cdot 30}{ 5! } \\\\ &=& \dfrac{30}{5} \cdot \dfrac{29}{4} \cdot \dfrac{28}{3} \cdot \dfrac{27}{2} \cdot \dfrac{26}{1} \\\\ &=& \dfrac{30}{5} \cdot \dfrac{29}{1} \cdot \dfrac{28}{4} \cdot \dfrac{27}{3} \cdot \dfrac{26}{2} \\\\ &=& 6 \cdot 29 \cdot 7 \cdot 9 \cdot 13 \\\\ &=& \mathbf{142506} \\ \hline \end{array} \)

 

laugh

 Oct 5, 2016

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