Double 11 Day, Bachelor Day Promotion!

Do you know that today (11/11) is a special festival during recent years in China. With four characters of “1”, this date was named as Bachelor’s Day. On this day, young people will hold bachelor parties to create couples or simply have fun. Some choose to end their bachelor life by showing love or proposing for marriage.

In 2009, Alibaba held the first Double Eleven Shopping Festival on Taobao.com, storming the online shopping for the very first time. Three years later, with coming 2012's Bachelor’s Day, more than 10,000 businesses, cooperating with e-commerce sites, are poised to rock the shopping festival again.Participants took actions to meet this festival.

Anyway, that's not what we gonna discuss today. We found this interesting question (listed below) that requires a careful analyse on the information provided and some calculation. Can you work it out? And how long it takes you to work it out?

'Ming wants to buy a sweater valued at $399. He already paid a deposit of $20.

If he paid deposit between 12pm – 2pm, the deposit can be tripled the actual amount that’s been paid and be used as a voucher. If he paid deposit after 2pm, then the deposit can be used as a voucher valued at $50.

On top of the voucher, if you can be the first 500 customer who pay the balance amount, the deposit you have paid can be returned.

Meanwhile, the store also runs promotions as the following:

Promotion A:

‘Deduct $20 when spend $399 and deduct $10 when spend $379’ provided ‘deposit amount + balance amount - triple value voucher is no less than the value of the above mentioned promotion.

Promotion B:

‘Deduct $20 when you spend $379 or deduct $10 when you spend $279, provided that ‘balance amount – triple value voucher is no less than the value of the above mentioned promotion.’

Condition: Voucher and promotion can only use once each. They can not be accumulated!

Question: What will be the lowest cost for Ming to buy the sweater?

此题的中文原题如下：

‘小明想在双十一买价值399的卫衣。

已付定金20元，且定金有三倍膨胀活动，但活动时间是0点~2点。2点以后定金可以抵用50元。

有付尾款前500免定金活动，同时该店铺有399减20和299减10的优惠券，其规则是“定金+尾款-定金膨胀优惠金额”大于等于“优惠券使用门槛”。

还有一种379减20和279减10的折扣券，其规则是“尾款-定金膨胀优惠金额”大于等于“折扣券面额”。

优惠券和折扣券只能选一种。

求，小明最后买到这件卫衣最少需要多少钱？’