设x双袜子时两种方案一样x100x100x100180*x+5（x－40）＝（180*10+5x）*90%
x100x100x100x100x100x100x100x100x100x100x100x100x100x100x100x1001600+5x＝1620+4.5x
x100x100x100x100x100x100x100x100x100x100x100x100x100x100x100x100x1000.5x＝20
x100x100x100x100x100x100x100x100x100x100x100x100x100x100x100x100x100x100x＝40
x100x100x100x100x100买40双袜子两种优惠方案的钱一样多
x100当x＝50时x100x100x100第一种x1001600+5x＝1600+250＝1850
x100x100x100x100x100x100x100x100x100第二笚x1001620+4.5x＝1620+225＝1845
x100x100应该选第二种方案