а)18/19-7/19+3/19: б)2/7+4/7-5/7: в)9/11-3/11-2/11: г)5/12+3/12+3/12 д)11/15-(3/15+7/15) е)13/16-(13/16-3/16).

18/19-7/19+3/19=14/192/7+4/7-5/7=1/79/11-3/11-2/11=4/115/12+3/12+3/12=11/1211/15-(3/15+7/15)=11/15-10/15=1/1513/16-(13/16-3/16)=13/16-10/16=3/16