1/2 + 1/6 + 1/12 + 1/20 + ...... + 1/930= (1 - 1/2) + (1/2 - 1/3) + (1/3 - 1/4) + ...... + (1/30 - 1/31)= 1 - 1/31= 30/31
6分之5
