12分之一+20分之一+30分之一+42分之一+56分之一+72分之一=多少？

Answer 1

12分之一+20分之一+30分之一+42分之一+56分之一+72分之一=多少？

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

Answer 2

1/12+1/20+1/30+1/42+1/56+1/72
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1/3-1/9
=2/9
注：1/[n×(n+1)]=1/n-1/(n+1)

Answer 3

原式=1/12+1/20+1/30+1/42+1/56+1/72
=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1/3-1/9
=3/9-1/9
=2/9
注：1/[n×(n+1)]=1/n-1/(n+1）

Answer 4

1/12＋1/20+1/30+1/42＋1/56+1/72
＝5／60＋3/60＋2/60＋1/42＋1/56＋1/72
＝1/6＋1/42＋1/56+1/72
＝7／42＋1/42＋1/56+1/72
＝4／21＋1/56＋1/72
＝32／168＋3/168＋1/72
＝5／24+1/72
＝15/72+1/72
＝2/9

Answer 5

等于6/72+1/72+3/60+2/60+1/42+1/56＝7/72+1/12+1/42+1/56＝7/72+7/84+2/84+1/56＝7/72+3/28+1/56＝7/72+6/56+1/56＝7/72+7/56＝49/504+63/540＝112/504＝2/9