Question 990553



S = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20}


C(20,5) = 20!/(20 - 5)!5!


= 20!/15!5!


= 2,432,902,008,176,640,000/(1,307,674,368,000)*(120)


= 15, 504 different 5 element subsets.