设鸡为X,鸭为80-x
2[x-0.2x]=3[80-x+12]
2x-0.4x=240-3x+36
1.6x=276-3x
1.6x+3x=276
4.6x=276
x=60
80-60=20
答：鸡为60,鸭为20.
哎!小学作业