设甲鱼苗x尾,乙鱼苗(6000-x)尾
(1)0.5x+0.8(6000-x)=3600
解得x=4000
所以甲鱼苗4000尾,乙鱼苗2000尾
(2)0.5x+0.8(6000-x)=2000(且x