刚刚开始看数学，有几道prep08弱题求助，恳请大牛指点！ DS: Is M+Z>0? (1) M-3Z>0 (2) 4Z-M>0 PS: If X is positive, which of the following could be the correct ordering of 1/X, 2X and X^2? (i) X^2 < 2X < 1/X (ii) X^2 < 1/X < 2X (iii) 2X < X^2 < 1/X PS: At a dinner party, 5 people are to be seated around a circular table. Two seating arrangements are consider different only when the positions of the people are different relative to each other. What is the total number of different possible seating arrangements for the group? -- by 会员 2012冲刺317 (2012/2/19 11:14:39)
No 1
I did wrong also. any 1 or 2 alone is not sufficient. do you agree?
If combined, 1+2 can deduce that z>0
and then 3z<m<4z, so m>0
Obviously, 1+2 sufficient
No 2
pay attention to could be
1/X, 2X and X^2
if x>1, could be 1/x<2x< x^2
if 0<x<1, could be x^2 < 2x < 1/x or x^2 < 1/x < 2x
if x<-1, could be 2x<1/x<x^2
if -1<x<0, could be 1/x<2x<x^2
(i) X^2 < 2X < 1/X
(ii) X^2 < 1/X < 2X
(iii) 2X < X^2 < 1/X
So iii is impossible. i and ii is maybe true.
No 3
first, just consider in the ordinary mode, it is clear that should be 5*4*3*2*1 = 120
then, consider the overlapped part under the circumtance.look below:
ABCDE should be same as BCDEA, CDEAB, DEABC and EABCD
So 120/5=24 | 
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发表于 2012-2-19 11:14:39
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