Răspuns :
1-2+3-4+5-6+7-8+9.........-18+19-20
1+3+5+7+9+11+13+15+17+19=100
-2-4-6-8-10-12-14-16-18-20=-110
100-110=-10
1+3+5+7+9+11+13+15+17+19=100
-2-4-6-8-10-12-14-16-18-20=-110
100-110=-10