De quantas maneiras se podem escolher 3 itens de 7? ((73)\binom{7}{3}(37))
(73)=7!3!4!=7×6×53×2×1=35\binom{7}{3} = \frac{7!}{3!4!} = \frac{7 \times 6 \times 5}{3 \times 2 \times 1} = 35(37)=3!4!7!=3×2×17×6×5=35