求教3道数学题，最好能翻译下

leokingdom

陈向东书上的机考模拟150题

32.ten flash cards,numbered 1 through 10 , 按升序排列,remove 2 and 4 ,how many different correct arrangments of four randomly selected cards are possible?  answer  :70

37.candy hearts were marked down from 30%-50% on 情人节. the following day, CH were marked down an additional 25% .问原来28刀的CH最低的多少就能买到？  答案 7刀  我怎么觉得是12.6呢？？

47.一个体育场里，4/5的SEAT in lower deck were sold , 如果1/4 of all the seating in 体育场is located in the lower deck ,and if 2/3 of all the seats in the 体育场were sold,what fraction of the unsold seats in the 体育场were in the lower deck?

answer  3/20

大牛们帮忙解答下 最好附带翻译下KEY WORD

leokingdom

大牛们帮忙解答下吧，不会……