Prep里的2道题及其他问题

Douzizi

1. are at least 10% of the ppl in placeA who are 65 years old or older employed? (B)
 1)11.3% of the population is 65 years or old or older
 2) of the population 65 years old or older, 20% of the men and 10% of the woman are employed

2. if the average (mean) of 4 different number is 30, how many of the numbers are greater than 30? (B)
 1)none of the 4 numbers is greater than 60
 2)2 of the 4 numbers are 9 and 10 respectively

3. how many of the 12 listed amounts are within 1.5 standard deviations of the mean? "with..."后面这句是什么意思？

4. 如果P=4n (n为质数）且P=3m(m为正整数），则如何确定P的值？

多谢了！

carollin2

1. B.
          0.2X+0.1y>=?0.1(X+Y)
          0.1(2X+Y)>=?0.1(X+Y)
          2X+Y>=X+Y
2. C
       0.25(a+b+c+d)=30; a+b=19
       c+d=101
       if c=30, d=71. but c,d<=60
       so c,d>30

3. within 1.5 standard deviation = 在1.5标准差之内

4. p = 12 I (I 为正整数)

Douzizi

谢谢Carollin!!!
第2题好有技巧哦，我自己是怎么也看不出来，不知道要练到什么时候才可以，sigh...

Douzizi

确认了一下第2题答案应该是B，不是C哎... 求解答...

Padmeelena

我做第二题也做不出B来,答案会不会有错啊

Padmeelena

3. how many of the 12 listed amounts are within 1.5 standard deviations of the mean? 这题怎么求啊?能不能把原题发过来看看啊?是拿均值-1.5吗?

Douzizi

我想Prep的答案不大会错吧...

第3题的题目比较长，我大概概括一下：列出了12个数，并告知mean of 8.1, standard deviation of 0.3, 问"how many of the 12 listed amounts are within 1.5 standard deviations of the mean"。 根据Carollin的提示，我的理解是取(（8.1-1.5x0.3), (8.1+1.5x0.3))之间的数即可。