解：
为方便计算，令A=1/2+1/3+1/4+1/5
则A=(30+20+15+12)/60=77/60
(1+1/2+1/3+/1/4+1/5)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5+1/6)
=(1+A)A-(1+A+1/6)(A+1/6)
=A(A+1)-(A+1/6)(A+7/6)
=A^2+A-A^2-7A/6-A/6-7/36
=-A/3-7/36
=-77/180-35/180
=-112/180
=-28/45
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