设鸭蛋x个,鸡蛋y个,则鸟蛋有100-x-y个 ∴3x+1y+0.1(100-x-y)=100 3x+y+10-0.1x-0.1y=100 29x+9y=900 29x=900-9y ∴x是9的倍数,且 x