请教prep 2套里Math 4道题，谢谢，急呢~

1. Amy's grade was the 90th percentile of the 80 grades for her class.Of the 100 grades from another class, 19 were higher than Amy's, and the rest were lower. If no other grade was the same as Amy's grade,then Amys grade was what percentile of the grades of the two classes combined?
A 72nd   B80th   C81th   D 85th E 92nd            Key : D

2.DS: Is the three-digit number N less than 550?
1) the product of the digits in N is 30
2) the sum of the digit s in N is 10                      Key:C

难道1)不充分么？

3.DS:  x,3,1,12,8
If x is an integer, is the median of the 5 numbers shown greater than the average of the 5 numbers?
1) x>6
2) x is greater than the median of the 5 numbers.                        key:E

为什么不选C呢?    我的思路是
排序 1，3，8，12  then 由1)推出x 可以在3，8间or 在8之后
当x在3，8间，median =x
当x在8之后 median =8

average = (1+3+8+12+x)/5=(24+x)/5

由2)推出  x在8之后 median =8  当x=6的时候  average = 6 ， x>8时  median=8>average
    

4. Five pieces of wood have an average length of 124 centimeters and a median length of 140 centimeters. What is the maximum possible length, in centimeters, of the shortest piece of wood?
A 90 B 100 C 110 D 130 E 140               key : B

擦汗，快考试了，今天做了第二套prep，上传图看不清楚，浪费大家时间，正好作文没练，我就当是练习打字了，

以上4道题，谢谢各位先，帮忙答疑哦~~急呢~

帮帮忙~~~~~

第3題:

X也有可能大於12阿...所以也有可能是無限大....so

應該是E沒錯

第四題:

因為全部長是620,扣掉median140剩480要給4個數,最小的那ㄍ要最大表示說median後的兩位要跟median一樣, 而第二小的那ㄍ要跟最小的一樣大,這樣才能使最小的那ㄍ極大化

就是 100 , 100, 140, 140, 140

第二題我想法跟你一樣.....愛莫能助

第一題我也愛莫能助.....

1. Amy's grade was the 90th percentile of the 80 grades for her class.Of the 100 grades from another class, 19 were higher than Amy's, and the rest were lower. If no other grade was the same as Amy's grade,then Amys grade was what percentile of the grades of the two classes combined?
A 72nd   B80th   C81th   D 85th E 92nd            Key : D

Amy's grade was the 90th percentile of the 80 grades for her class.说明在她前面有80*0.1=8个人

（8+19）/(80+100)=0.15 15%的人高于Amy 所以她处在85percentile 不知对不？

明白了明白了，谢谢谢谢

还有第2题咧？？？

第二题条件1 不充分呢

3个数字 1，5，6当组合成651或者561的时候就不成立了哦

所以要补充条件2，3个加起来为10排除了条件1不成立的情况。

确定为2，3，5的组合，选C