42. 

John and Mary own shares of stock in a certain company.   Does John own more shares of the company's stock than Mary?
 
(1) Mary owns more than 500 shares of the company's stock.
 
(2) The number of shares of the company's stock that John owns is 400 less than twice the number of shares of the
company's stock that Mary owns.
 

由1得Mary>500，由2得John=2Mary-400,联合1 2得John>600,Mary>500   答案选C，可是我觉得没法判断一定J>M啊~~？

84.  7517-!-item-!-187;#058&005572
If p is a prime number greater than 2, what is the value of p ?
 
(1)      There are a total of 100 prime numbers between 1 and p + 1.
 
(2)      There are a total of p prime numbers between 1 and 3,912.
 

不知道怎么下手了~~

57. 

During a sale, for each shirt that Mark purchased at the regular price, he also purchased a shirt at half the regular price.   这句的意思是只有一件shirt是half the regular price，其余的都是 regular price吗？
How many shirts did Mark purchase during the sale?
 
(1)    The regular price of each of the shirts that Mark purchased during the sale was $21.50.
 
(2)    The total of the prices for all the shirts that Mark purchased during the sale was $129.00.

84题只要P能够是一个确切值就行，所以D

57题是C，你题意理会错了，意思是买一件正价，就可以用半价买第二件，这就是商场里面所谓的第二件半价销售策略。

1肯定不能得出件数

2可以算出86块钱买了正品，43块买了半价，但由于不知道单价，所以不知道件数

二者联立，发现86能被21。5整除，所以C对

42题，可以设M为x，则J就为2x-400

题目问J是否大于M

就用2x-400-x看是否大于0

2x-400-x=x-400

由(1)得x〉500

所以x-400肯定大于0

就能证明J〉M