Cu 1 duong thang cat 100 duong thang con lai thi tao thanh 100 giao diem. Ma co 101 duong thang nhu the nen co tat ca:
101.100=10100 (giao diem)
Nhung moi duong thang duoc tinh 2 lan nen co tat ca:
10100:2=5050(giao diem)
Vay co tat ca 5050 giao diem.
Cu 1 duong thang cat 100 duong thang con lai thi tao thanh 100 giao diem. Ma co 101 duong thang nhu the nen co tat ca:
101.100=10100 (giao diem)
Nhung moi duong thang duoc tinh 2 lan nen co tat ca:
10100:2=5050(giao diem)