1+3+5+7+9+...+99 1-2+3-4+5-6+7-8+...-100 -100-99-98-...-2-1-0+1+2+...+48+49+50

1. 50/2 x 100 = 2500
2. (1 + 3 + 5 + 7 + .... + 99) - (2 + 4 + 6 + 8 + .... + 100) =
2500 - (100/2 x 51) =
2500 - 2550 = -50
3. 100/2 x (-101) + 50/2 x 51 = -5050 + 1275 = -3775