设x一班男生x人,二班男生y人,全部男生z人,三班女生a人x+y=3/5z,(2/5)z+a=x+y,(2/5)z+a=3/5z,a=1/5z,x+y+a=3(x+y)-z,x+y+1/5z=3(x+y)-z,1/5z=2(x+y)-z,z=10(x+y)-5z,6z=10(x+y),z=5/3(x+y)a=1/3(x+y)[x+y+1/3(x+y)]...