3/4+1/20+1/30+1/42+1/56+1/72 求如何简便计算快啊!!!!!!!!!!!!

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3/4+1/20+1/30+1/42+1/56+1/72 求如何简便计算快啊!!!!!!!!!!!!
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3/4+1/20+1/30+1/42+1/56+1/72 求如何简便计算快啊!!!!!!!!!!!!
3/4+1/20+1/30+1/42+1/56+1/72 求如何简便计算
快啊!!!!!!!!!!!!

3/4+1/20+1/30+1/42+1/56+1/72 求如何简便计算快啊!!!!!!!!!!!!
3/4+1/20+1/30+1/42+1/56+1/72
=3/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1-1/9
=8/9
如果本题有什么不明白可以追问,

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

不懂可追问
满意请采纳
谢谢

1/20=1/4-1/5
1/30=1/5-1/6
1/42=1/6-1/7
1/56=1/7-1/8
1/72=1/8-1/9

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