1 / 6 = 1 / 2-1 / 3, 1 / 12 = 1 / 3-1 / 4, 1 / 20 = 1 / 4-1 / 5. According to the above rules, calculate the following question. 1 / 6 + 1 / 12 + 1 / 20 + 1 / 30 + 1 / 42 + 1 / 56 + 1 / 72

1/6+1/12+1/20+1/30+1/42+1/56+1/72
=1/2-1/3+1/3-1/4+1/4-1/5+.+1/8-1/9
=1/2-1/9
=9/18-2/18
=7/18

1 / 2 = 1-1 / 2 1 / 6 = 1 / 2-1 / 3 1 / 12 = 1 / 3-1 / 4... Calculate the following question according to the above rule: 1 / 2 + 1 / 6 + 1 / 12 + 1 / 20 + 1 / 30=

Original formula = (1-1 / 2) + (1 / 2-1 / 3) + (1 / 3-1 / 4) + (1 / 4-1 / 5) + (1 / 5-1 / 6)
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6
=1-1/6
=5/6

1/6+1/12+1/20+1/30+1/42+1/56
=(1/2--1/3)+(1/3--1/4)+(1/4--1/5)+(1/5--1/6)+(1/6--1/7)+(1/7--1/8)
=(1/2)--(1/8)
=(4/8)--(1/8)
=3/8.