(+13/17)-(+3又1/2)+(-1又1/5)-(-2又1/2)+4/17-2又4/5
=13/17-3-1/2-1-1/5+2+1/2+4/17-2-4/5
=13/17+4/17-3-1+2-2-1/2+1/2-1/5-4/5
=17/17-4+0+0-5/5
=1-4-1
=-4