Question

Sa se calculeze numarul submultimilor ordonate cu 4 elemente ale unei submultimi care are 8 elemente

Answer 1

$A_8^4 = \frac{8!}{(8-4)!} = \frac{8!}{4!} = \frac{4!*5*6*7*8}{4!} = 5*6*7*8=1680$

Answer 2

$\begin{array}{rcl}C_{8}^4 &=& \dfrac{8!}{4!(8-4)!} = \dfrac{8!}{4!\cdot 4!} = \dfrac{4!\cdot 5\cdot 6\cdot 7\cdot 8}{4!\cdot 1\cdot 2\cdot 3\cdot 4} = \\ \\ &=& 5\cdot 7\cdot 2} = 35\cdot 2 = 70\end{array}$