急问几道prep题

1. If x is a positive number less than 10, is z greater than the average (arithmetic mean) of x and 10 ?

(1) On the number line, z is closer to 10 than it is to x.

(2) z = 5x
  
Answer:A

2. A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture that was 5 percent gravel G, by weight.  What is the value of x ?

(1) y = 10

(2) z = 16
    
Answer: D

3. Machines X and Y work at their respective constant rates.  How many more hours does it take machine Y, working alone, to fill a production order of a certain size than it takes machine X, working alone?

(1) Machines X and Y, working together, fill a production order of this size in two-thirds the time that machine X, working alone, does.

(2) Machine Y, working alone, fills a production order of this size in twice the time that machine X, working alone, does.

Answer: E

这几道我已经在prep汇总的帖子里面搜索了，但是没有搜索到啊？请各位NN们给解释一下，或者你们找到的以前解释的link，谢啦

第一題畫數線就知道 A可以 B如果X=1 Z=5 mean(1+10)/2=5.5 比Z還大 not sufficient

第三題之前做OG裡面常常提到the clues does not provide any specific numbers

所以你算不出他要求的正確小時的數字

哦，谢啦，那么第二题呢？