cho A :{1,2,3,4,5,6}tu` A co' the? lap dc bao nhieu so' co' 6 chu~ so' khac' nhau va` tinh' tong? cua? cac' so' nay`?????????????
lam` di nha cac' ban!
lap 6 chu so khac nhau thi de roi con tinh tong tui chua nghi ra
vay lam truoc nha
gia su so do co dang abcdef
a co 6 cach chon
ung voi moi cach chon a ta co 5 cach chon b
...............................a,b.........4....................c
..............................a,b,c........3..................d
..............................a,b,c,d........2...............e
..........................a,b,c,d,e.............1...........f
so cach chon so co 6 chu so khac nhau la 5!=120