简便运算（题目在下面）

更新时间2018-07-13 17:51:02

原式=(5-2)/(2*5)+(7-5)/(5*7)+...+(17-13)/(13*17)+(23-17)/(17*23)

=(1/2-1/5)+(1/5-1/7)+...+(1/13-1/17)+(1/17-1/23)

=1/2-1/5+1/5-1/7+...+1/13-1/17+1/17-1/23

=1/2+(-1/5+1/5)+(-1/7+1/7)...+(-1/13+1/13)+(-1/17+1/17)-1/23

=1/2-1/23

=(23-2)/2*23

=21/46

145135/380926

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