设山羊为X只，则绵羊为800-XX40%-(800-X)50%=50解得X=500则800-500=300所以山羊有500只，绵羊有300只
设绵羊为x，山羊为y由题意得: x+y=800 ① 0.4y=0.5x+50 ②由①和②可得：0.4*（800-x）=0.5x+50 320-0.4x=0.5x+50 0.9x=270 x=300 y=500
