1/2,1/3,1/4,1/5,…… 1 / 90, 1 / 91, pick out ten numbers, add the sign, and their sum is - 1

1/2,1/3,1/4,1/5,…… 1 / 90, 1 / 91, pick out ten numbers, add the sign, and their sum is - 1

∵ 1 / 12-1 / 4-1 / 5-1 / 20-1 / 6-1 / 7-1 / 42-1 / 8-1 / 9-1 / 72 = 1 / 12 - (1 / 4 + 1 / 5 + 1 / 20) - (1 / 6 + 1 / 7 + 1 / 42) - (1 / 8 + 1 / 9 + 1 / 72) = 1 / 12-10 / 20-14 / 42-18 / 72 = 1 / 12-1 / 2-1 / 3-1 / 4 = 1 / 12-6 / 12-4 / 12-3 / 12 = - 1, so the ten numbers are: 1 / 12,1 / 4,1 / 5,1 / 20,1 / 6,1 / 7