根据1/12=1/3-1/4的规律计算下题1/12+1/20+1/30+1/42+1/56,

1/12+1/20+1/30+1/42+1/56
＝（1/3--1/4）+（1/4--1/5）+（1/5--1/6）+（1/6--1/7）+（1/7--1/8）
＝1/3--1/8
＝5/24.

1/12+1/20+1/30+1/42+1/56=1/3-1/8=5/24

1/12+1/20+1/30+1/42+1/56
=(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)
=1/3-1/8
=5/24
(以上回答，满意请采纳！)

1/12+1/20+1/30+1/42+1/56
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8
=1/3-1/8
=8/24-3/24
=5/24

1/20=1/4-1/5
1/30=1/5-1/6
以此类推
1/12+1/20+1/30+1/42+1/56
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8
=1/3-1/8
=5/24

1/12＝1/3-1-4，那么1/20＝1/4-1/5，1/30＝1/5-1/6，1/42＝1/6-1/7,1/56＝1/7-1/8，全部相加就是1/3-1/8＝5/24