Question

Numărul submultimilor cu 4 elemente ale multimi cu 7 elemente

Answer 1

$C_{7} ^{4} = \frac{7!}{4!(7 - 4)!} = \frac{1 \times 2 \times 3 \times 4 \times 5 \times 6 \times 7}{(1 \times 2 \times 3 \times 4) \times 3!} = \frac{5 \times 6 \times 7}{1 \times 2 \times 3} = \frac{5 \times 2 \times 7}{1 \times 2} = \frac{5 \times 7}{1} = \frac{35}{1} = 35$