prep maths 看不懂题目

EthanEthan

70,75,80,85,90,105,105,130,130,130The list shown consists of the times, in seconds, that it took each of 10 schoolchildren to run a distance of 400 meters. If the standard deviation of the 10 running times is 22.4 seconds, round to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times?
A. One
B. Two
C. Three
D. Four
E. Five


Answer B

honeypony

1 肯定对撒，没得问题吧~~2，y是整数，所以，Y小于1时Y就是0或者是负整数。
然后分析撒，
如果X大于0，y=2x 也大于0，不成立撒，
X小于0，y等于0，对了撒
所以是D撒

EthanEthan

接连还有一题prep,怀疑是不是prep题目问题
If y is an integer and y=|x|+x, is y=0?
(1) X<0
(2) y<1
答案选D.请问 y<1同样可以推出y=0麽?还是题目本身是x is an integer?

EthanEthan

谢谢! 嗯,看来就是没读懂题目.再多问一句,more than 1 standard deviation below是否有n个standard deviation的说法?

honeypony

LZ就是没看懂题，我觉得，题目就是问，这10个小P孩的跑步时间，有多少

个低于 mean减去一个标准差~~~
平均数是100，标准差是22.4,100-22.4=77.6，选出来有两个，选B，我觉得是

这个意思，欢迎拍~~