题目有误,应为：
5/1*2*3*4+7/2*3*4*5+9/3*4*5*6+.+17/7*8*9*10
=1/1*3-1/2*4+1/2*4-1/3*5+1/3*5-1/4*6+.+1/7*9-1/8*10
= 1/1*3-1/8*10
=1/3-1/80
=77/240 题目有误,应为：
5/1*2*3*4+7/2*3*4*5+9/3*4*5*6+.+17/7*8*9*10
=1/1*3-1/2*4+1/2*4-1/3*5+1/3*5-1/4*6+.+1/7*9-1/8*10
= 1/1*3-1/8*10
=1/3-1/80
=77/240