如何算1x1\4+1\4x1\7+1\7x1\10+1\10x1\13+1\13x1\16

1 * 1/4 + 1/4 * 1/7 + 1/7 * 1/10 + 1/10 * 1/ 13 + 1/13 * 1/16= (1- 1/4) / 3 + (1/4 - 1/7) / 3 + (1/7 - 1/10) / 3 + (1/10 - 1/13) / 3 + (1/13 -1/16) / 3= [(1- 1/4) + (1/4 - 1/7) + (1/7 - 1/10) + (1/10 - 1/13) + (1/13 -1/16)] / 3= [1 + (-1/4 + 1/4) + (-1/7 + 1/7) + (-1/10 + 1/10) + (-1/13 + 1/13) - 1/16] / 3= [1 - 1/16] / 3 = [15/16] / 3= 5/16