De qua
Chon 1 trong 8 diem noi voi 7 diem con lai lam nhu the voi 8 diem ta duoc:8.7=56(diem)
Nhung moi duong lap lai 2 lan nen ta duoc:56:2=28(diem)
k cho minh nhe
neu la n diem ta se ve duoc n(n-1)/2 duong thang.co 8 diem ve duoc 8(8-1)/2=8.7/2=28 duong thang.