设成本价为X,则标价为X*(1+p%)降价后X*(1+p%)*(1-d%)>=X解不等式有d<=100-100/(1+p%)
成本是A(1+p%)(1-d%)大于或者等于A即1-d%>=1/(1+p%) 即d%=1-1/(1+p%)=p%/(1+p%)
设商品的成本为单位1,则原价为1+p,可列方程(1+p)(1-d)=1,解方程得d=1-1/(1+P)
成本X,则标价(1+p%)X则X=(1+p%)X*(1-d%)则d=p/(100+p)
1/(1+p%)