According to the following law, such as 1 / 2 = 1-1 / 2, 1 / 6 = 1 / 2-1 / 3, 1 / 12 = 1 / 3-1 / 4 1/6+1/12+1/20+1/30+1/42

According to the following law, such as 1 / 2 = 1-1 / 2, 1 / 6 = 1 / 2-1 / 3, 1 / 12 = 1 / 3-1 / 4 1/6+1/12+1/20+1/30+1/42

1/6+1/12+1/20+1/30+1/42
=(1/2-1/3)+(1/3-1/4)+1/4-1/5+1/5-1/6+1/6-1/7
=1/2-1/7
=5/14

It is known that 5 / 6 = 1 / 2 + 1 / 3, 7 / 12 = 1 / 3 + 1 / 4, 9 / 20 = + 1 / 4 + 1 / 5
1 + 2 1-6 5 + 12 7-20 9 + 30 11-42 13 + 56 15

1+1/2-5/6+7/12-9/20+11/30-13/42+15/56
=1+1/2-(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+1/8
=9/8
=1.125

It is known that 5 / 6 = 1 / 2 + 1 / 3, 7 / 12 = 1 / 3 + 1 / 4, 9 / 20 = 1 / 4 + 1 / 5
Calculate 1 + 2 of 1-6 of 5 + 12 of 7-20 of 9=

Big brother, it's four fifths of what we know