Gmatprep 几道数学题Help!

Resident in Town X hold a survey determine number of hours per week they spent in watching TV. The result of survey had a mean of 21 hours and standard deviation of 6 hours. The number of hour Pat spent in watching TV last week was between 1 and 2 standard deviation below the mean. Which of the following could be the number of hours Pat spent on TV last week?
A. 30 B. 20 C 18 D12 E6

一遇到方差问题光想着套公式：d^2=[(a1-a)^2+(a2-a)^2+....+(an-a)^2 ]/n xdjm help!

DS
On a certain sight-seeing tour, the ratio of the number of women to the number of children was 5 to 2. What was the number of men on sight-seeing tour?
1) on the sight -seeing tour, the ratio of the number of children to the no of men was 5 to 11
2)the number of women on the sight-seeing tour was less than 30.
Key is C

My reasoning is 1) alone can not conclude the number of men because there is no specific number given no matter children, women or men. 2) can not conclude the number of men either only by providing a range of women's no. 1)&2) together can't not leading the number because the number of women is not specific... Help to see how my reasoning went wrong!

最后弱问一句为什么Gmatprep不可以copy &paste? 导致作文浪费时间在重复original statement