题目内容：

1/30+1/42+1/56+1/72简便算法是?

优质解答

1/30+1/42+1/56+1/72
=1/5*6+1/6*7+1/7*8+1/8*9
=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1/5-1/9
=9/45-5/45
=4/45