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！

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...

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。