aX1/6-1/6b=1/6x(a-b)=1/6x[(1/2+1/3+1/4+1/5)-(1/3+1/4+1/5)]=1/6x1/2=1/12
(1/2+1/3+1/4+1/5)×(1/3+1/4+1/5)+(1/2+1/3+1/4+1/5)×1/6-(1/2+1/3+1/4+1/5)×(1/3+1/4+1/5)-1/6*(1/3+1/4+1/5)=1/2*1/6=1/12
a×(b+1/6)-(a+1/6)×b=a×1/6-1/6×b=1/6*(a-b)=1/6*((1/2+1/3+1/4+1/5)-(1/3+1/4+1/5))=1/6*1/2=1/12
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