(1/3)-(1/12)-(1/20)-(1/30)-(1/42) = 等于多少 减去二十分之一减去三十分之一减去四十二分之一就是(1/3)-(1/12)-(1/20)-(1/30)-(1/42) =

(1/3)-(1/12)-(1/20)-(1/30)-(1/42) = 等于多少 减去二十分之一减去三十分之一减去四十二分之一就是(1/3)-(1/12)-(1/20)-(1/30)-(1/42) =
(1/3)-(1/12)-(1/20)-(1/30)-(1/42) = 等于多少 减去二十分之一减去三十分之一减去四十二分之一
就是(1/3)-(1/12)-(1/20)-(1/30)-(1/42) =

(1/3)-(1/12)-(1/20)-(1/30)-(1/42) = 等于多少 减去二十分之一减去三十分之一减去四十二分之一就是(1/3)-(1/12)-(1/20)-(1/30)-(1/42) =
(1/3)-(1/12)-(1/20)-(1/30)-(1/42)
=1/3 -(1/12+1/20+1/30+1/42)
=1/3-(1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)
=1/3-(1/3-1/7)
=1/7

1/4
小学生同学请你好好学习,不要问这么简单的东西.
1/12 = 1/3-1/4
1/20 = 1/4-1/5
1/30 = 1/5-1/6
所以原式= 1/3-(1/3-1/4) - (1/4-1/5)-(1/5-1/6)-(1/6-1/7) = 1/7