设获利为y
y={800-20(x-60)} * ( x-50 )
=(2000-20x)*(x-50)
= -20(x-100) * (x-50)
=-20(x2-50x-100x+5000)
=-20(x2-150x+5000)
获利为12000
-20(x2-150x+5000)=12000
x2-150x+5000+600=0
x2-150x+5600=0
(x-75)2=5
x1=80 x2= 70
进货量800-20(x-60)
x1 400
x2 600
成本
x1 =400*50 =20000
x2 =600*50 =30000
所以单价定为80 进400件