[求助]求助几道prep-2 DS题

tina0515

122.   12685-!-item-!-187;#058&009461

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

 

(1)  2 is not a factor of n.

 

(2)  3 is not a factor of n.

133.   14229-!-item-!-187;#058&010329

What is the average (arithmetic mean) height of the n people in a certain group?

 

(1)  The average height of the  tallest people n the group is 6 feet 2
                         inches, and the average height of the rest of the people n the group is f feet 10 inches.

 

(2)  The sum of the heights of the n people is 178 feet 9 inches.

为什么不是D？

jmc0966

133--中的1和2条件中，都不知道N=?

所以不是D啊。

大胖

第122题，将（1）（2）结合起来，可以假设n=6k+1 或者6k-1 然后可证明能整除24.   lz可自己试试看。