x+y=m (1)5x+3y=31 (2)(2)-(1)*35x+3y-3x-3y=31-3m2x=31-3mx=(31-3m)/2y=m-x=m-(31-3m)/2解xy均是非负数x≥0,(31-3m)/2≥0,31-3m≥0,3m≤31,即m≤31/3y≥0,m-(31-3m)/2≥0,2m-31+3m≥0,5m≥31,即m≥31/5所以31/5≤m...