各位NN~请教两道PREP的数学题~急~谢谢

girasol0821

1.If n and y are positive integers and 450y=n^3,which of the following must be an integer?  
        y/3*2^2*5    y/3^2*2*5  y/3*2*5^2
   A.None
   B.
   C.
   D.
   E.
答案选B

2.The residents of Town X participated in a survey to determine the number of hours per week each resident spend watching TV.The distribution of the results of survey had a mean of 21hours and a standard deviation of 6 hours.The number of hours that Pat,a resident of Town X,watched TV last week was between 1 and 2 standard deviations below the mean.Which of the following could be number of hours Pat watch TV last week?
A.30
B.20
C.18
D.12
E.6
答案选D

快考试了，希望大牛们帮我看看啦，谢谢~

2.

jsmart

450y=3^2*5^2*2y=n^3
so，y至少是3*5*2^2的倍数，所以是第一个式子是整数

jsmart

第二题是说 mean-standard deviation<at那人看电视的时间<mean+standard deviation
so,D

girasol0821

谢谢~不过第二题我还是没怎么弄明白...能帮我再解释一下么？

jsmart

哦，我错了。。。我打错了。。。应该是mean-2standard deviationPat那人看电视的时间<mean-standard deviation


21-6*2<at那人看电视的时间<21-6

这回就明白了吧

girasol0821

恩恩~明白了~谢谢