(三分之二加五分之一)加(三分之二减十七分至十二)减(五分之一加十七分之五)
=(2/3+1/5)+(2/3-12/17)-(1/5+5/17)
=2/3+1/5+2/3-12/17-1/5-5/17
=(2/3+2/3)+(1/5-1/5)-(12/17+5/17)
=4/3+0-1
=1/3
(三分之二加五分之一)加(三分之二减十七分至十二)减(五分之一加十七分之五)
=(2/3+1/5)+(2/3-12/17)-(1/5+5/17)
=2/3+1/5+2/3-12/17-1/5-5/17
=(2/3+2/3)+(1/5-1/5)-(12/17+5/17)
=4/3+0-1
=1/3