原式=1×(1/3+1/4+1/5)+(1/3+1/4)×(1/3+1/4+1/5)-[1×(1/3+1/4)+(1/3+1/4+1/5)×(1/3+1/4)]
=1×(1/3+1/4+1/5)+(1/3+1/4)×(1/3+1/4+1/5)-1×(1/3+1/4)-(1/3+1/4+1/5)×(1/3+1/4)
=1×(1/3+1/4+1/5)-1×(1/3+1/4)
=1/3+1/4+1/5-1/3-1/4
=1/5
望采纳
解:原式=(1/3+1/4)x(1/3+1/4+1/5)十(1/3+1/4+1/5)—(1/3+1/4+1/5)(1/3+1/4)一(1/3+1/4)
=1/3+1/4+1/5+1/3—1/4
=1/5