Question

1) A{1....6} Determinati numarul submultimilor cu cel putin cinci elemente sau cel mult doua elemente ale multimii A.
2) Determinati numarul submultimilor cu cel putin noua elemente ale multmii {1.....10}

Answer 1

$\displaystyle\\1)\\n=C_6^5 + C_6^6 = C_6^1 + C_6^6 = 6+1=7\text{ submultimi}\\\\2)\\n = C_{10}^9 + C_{10}^{10} = C_{10}^1 + C_{10}^{10} = 10+1=11\text{ submultimi}$