麻烦大家支招，请教prep几道题，多谢：）

justoneway

1，the function f is defined for all positive integers n by the following rule:f(n) is the number of positive integers each of which is less than n and has no prime number , then f(p)=

2,for any triangle t in the xy-coordinate plane, the center of t is defined to be the point whose x-coordinate is the average of the x-coordinates of the vertices of t and whose y-coordinate is the average of the y-coordinate of t. if a certain triangle has vertices at the points(0,0) and (6,0) and center at the point (3,2),what are the coordinates of the remaining vertex? 为什么我算出来时是（3，4），但是答案是（3，6）呢？

3 many bought several penciles, if each pencil was either a 23-cent pencil or a 21-cent pencil, how many 23 -cent pencil did mary buy?
  (1) mary bought total 6 pencils
  (2) the total volume of the pencil mary bought was 130 cents.
 我选c,可是答案是b,但是设方程21x+23y=130,两个未知数一个方程，怎样简便解答出来呢？

4 if mv<pv<0,is v>0?
   (1) m<p
   (2) m<0 答案是d, 我选a,第二个怎么成立呢？ -v<pv 怎样推出v>0呢？

5， the sum of the first 50 positive even integers is 2550, what is the sum of the even integers from 102 to 200，inclusive？

justoneway

up

paulstars

以下是引用justoneway在2008-7-12 6:59:00的发言：
1，the function f is defined for all positive integers n by the following rule:f(n) is the number of positive integers each of which is less than n and has no prime number , then f(p)=

2,for any triangle t in the xy-coordinate plane, the center of t is defined to be the point whose x-coordinate is the average of the x-coordinates of the vertices of t and whose y-coordinate is the average of the y-coordinate of t. if a certain triangle has vertices at the points(0,0) and (6,0) and center at the point (3,2),what are the coordinates of the remaining vertex? 为什么我算出来时是（3，4），但是答案是（3，6）呢？

3 many bought several penciles, if each pencil was either a 23-cent pencil or a 21-cent pencil, how many 23 -cent pencil did mary buy?
  (1) mary bought total 6 pencils
  (2) the total volume of the pencil mary bought was 130 cents.
 我选c,可是答案是b,但是设方程21x+23y=130,两个未知数一个方程，怎样简便解答出来呢？

4 if mv<pv<0,is v>0?
   (1) m<p
   (2) m<0 答案是d, 我选a,第二个怎么成立呢？ -v<pv 怎样推出v>0呢？

5， the sum of the first 50 positive even integers is 2550, what is the sum of the even integers from 102 to 200，inclusive？

4. mv<pv<0

   m<0 

上面两个条件一定得出v>0啊，否则两个负数如何相乘会produce 一个负数呢？负负得正，正负得负嘛

justoneway

多谢楼上，有朋友知道1，2，3怎样解答呢？多谢：）：）

justoneway

麻烦大家援手，1，5，多谢了：）：）