马上考试了紧急求问NN三道PREP数学题!!!

1

if n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24, what's the value of r ?

1.n is not divisible by 2

2.n is not divisible by 3

2

a set of 15 different intergers has a median of 25 and a range of 25. what's the greatest possible integer that could be in this set?

32  37  40  43  50

3

how many odd integers are greater than the integer X and less than the integer Y?

1.there are 12 even integers greater than X and less than Y

2.there are 24 integers greater than X and less than Y

how many odd integers are greater than the integer X and less than the integer Y?

1.there are 12 even integers greater than X and less than Y

2.there are 24 integers greater than X and less than Y

Answer: 1) 12 even ,可能有 13或者11,关键看X Y 是不是奇偶

        2) 24 integer, X Y 必定不同奇偶,因为是X+25=Y 所以,这24个中必定有一半是odd

选择B

OA呢

答案是B

我来答第二题 其实有选项不妨一个一个试试 既然问最大可能多少就从最大的50开始

如果是50最大 那么最小就是25（range是25） 显然不对 因为平均数也是25

接下来试试43 因为range是25 最小就是18 从18到25可以有18 19 20 21 22 23 24共七个不一样的整数对吧

那么25就是从小到大数的第8个 正好是中位数 所以43就是正确答案了

第2题我也做到了，是43.

因为15是中位数。就是从小到大排列后的第8个数。因为 max=min+range，要让最大的数达到最大，而range=25固定，就要使min最大，当数列是连续整数的时候，min最大，min=25-7=18.所以max=min+range=18+25=43.

答案是C 为什么啊?

1

if n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24, what's the value of r ?

1.n is not divisible by 2

2.n is not divisible by 3

选E 举反例 1=〉n为奇数，余数有三种情况，当(n-1)(n+1)<24, r=8;当(n-1)(n+1)>24, r=0或者1

2=〉随便举反例

1+2， 因为当(n-1)(n+1)<24, r=8，不然可确定r=1

2

a set of 15 different intergers has a median of 25 and a range of 25. what's the greatest possible integer that could be in this set?

32  37  40  43  50

43, 由第8个数为25， 可推得第1个数最大为25-（8-1）= 18， 所以最大的数为25+18=43