问一个数学问题，请大家答疑，谢谢。问题如下

A store's Cyber Monday promotion offers electronics at 28 to 70 percent discounted prices. During the promotion, Ali purchases a laptop that is discounted from $355.55 to $165.65. Assume that a 7.5 percent sales tax is included in all prices.

Which of the following approximates the percent discount of Ali's Cyber Monday laptop purchase?

A. 28%

B. 47%

C. 53% 

D. 70%

答案是B 47%. 355.55x = 165.55 x=0.466 

我的问题是为什么不是C 53%. (355.55-165.55)/355.55 = 0.5341

所有跟帖： 

• 7.5 percent sales tax -傻闷登儿- ♂ (0 bytes) () 08/11/2019 postreply 18:08:07

• 哪个是关键词？ -shiyishiwc- ♀ (0 bytes) () 08/11/2019 postreply 18:27:28

• 关键词是discount -数与形- ♀ (0 bytes) () 08/11/2019 postreply 18:35:52

• discount是指税前的价格，不是税后的价格。 -gegenion- ♂ (0 bytes) () 08/11/2019 postreply 18:31:05

• sale tax 是固定比例7.5%, 税前税后算折扣比例一样的 -眼镜- ♂ (0 bytes) () 08/11/2019 postreply 18:33:09

• You question has nothing to do with math, but a simple English. -czhz- ♀ (0 bytes) () 08/11/2019 postreply 19:44:13

• Your question -czhz- ♀ (0 bytes) () 08/11/2019 postreply 19:44:42

• 答案应该是C。 -数与形- ♀ (166 bytes) () 08/11/2019 postreply 18:33:44

• 这个找成功的兔家的数学娃看看， 他英文比俺们强 -眼镜- ♂ (0 bytes) () 08/11/2019 postreply 18:38:08

• 我相信他！ -眼镜- ♂ (0 bytes) () 08/11/2019 postreply 18:57:21

• Yes, he did screw it up. The problem description says x% discoun -czhz- ♀ (0 bytes) () 08/11/2019 postreply 19:50:59

• The problem description says x% discounted price, not x% off. -czhz- ♀ (0 bytes) () 08/11/2019 postreply 19:52:12

• and also use the "at" (at 20-70%), not off. -czhz- ♀ (0 bytes) () 08/11/2019 postreply 20:02:02

• at 28 to 70 percent discounted prices.(rephrase: it is a discoun -czhz- ♀ (0 bytes) () 08/11/2019 postreply 20:07:05

• (rephrase: it is a discounted price that is at the 20-70% level, -czhz- ♀ (0 bytes) () 08/11/2019 postreply 20:07:45

• so the answer should refer to that description. -czhz- ♀ (0 bytes) () 08/11/2019 postreply 20:08:42

• 这个答案是错的，想想看，通常我们看到10% discount知道意思是新价格是旧的90%， -数与形- ♀ (57 bytes) () 08/11/2019 postreply 18:38:17

• 同意，出题的人也许没仔细想想英文，就像中文里A比B大五倍不同于A是B的五倍，小学老师一再强调的，但大人往往混用 -musicbeginner- ♂ (0 bytes) () 08/11/2019 postreply 18:44:35

• you need to learn simple English, not the author. -czhz- ♀ (0 bytes) () 08/11/2019 postreply 19:53:42

• 觉得这个答案不对，才来问 -shiyishiwc- ♀ (0 bytes) () 08/11/2019 postreply 18:46:36

• 这个不是price，是 price 加税后的价格，只可以比较实质价格，而不是税后价格。 -笑薇.- ♀ (0 bytes) () 08/11/2019 postreply 19:49:11

• 这是 KALLIS SAT 的复习题 -shiyishiwc- ♀ (0 bytes) () 08/11/2019 postreply 18:49:03

• 建议放弃，误人子弟啊 -糖果果- ♀ (0 bytes) () 08/11/2019 postreply 18:55:48

• percent discount of Ali's Cyber Monday laptop purchase, 反正我理解是价格 -网恋无罪- ♂ (0 bytes) () 08/11/2019 postreply 19:02:02

• 便宜了（价格差）的百分比。就是多少百分比 off 的意思吧 -网恋无罪- ♂ (83 bytes) () 08/11/2019 postreply 19:04:02

• 谷歌了一下，就是价差/原价的百分比，percent off 同意 ，有图有真相 -网恋无罪- ♂ (127 bytes) () 08/11/2019 postreply 19:20:13

• 你还是继续在网上谈恋爱吧，至于学英语，还是找个好老师。 -czhz- ♀ (0 bytes) () 08/11/2019 postreply 20:25:44

• 觉得答案不对，来问问 -shiyishiwc- ♀ (0 bytes) () 08/11/2019 postreply 19:12:33

• please notice it is "at" not "off". -czhz- ♀ (0 bytes) () 08/11/2019 postreply 20:03:51

• B是对的，问的是便宜了多少百分比，而不是原价的多少百分比，跟税率无关。 -miniBit- ♀ (0 bytes) () 08/11/2019 postreply 21:31:00