两道关于standard deviation的,我实在是不明白这个standard deviation below the mean是什么意思?
1.The distribution of results of survay had a mean of 21hours and a standard deviation of 6. The number of hours of Pat(是一個人)watch tv last week was between 1 and 2 standard deviations below the mean. Pat上周可能看了多少小時的電視?
a.30 b.20 c.18 d.12 e.6
答案:d
2. 70,75,80,85,90,105,105,130,130,130
The list shown consists of the times, in seconds, that it took each of 10 school children to run a distance of 400 meters. If the standard deviation of the 10 running times is 22.4 seconds, rounded to the nearest tenth of a second, how many of the 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
3. DS If 500 is the multiple of 100 that is closest to X and 400 is the multiple of 100 that is closest to Y, which multiple of 100 is closest to X+Y?
1)x<500
2) y<400
ANSWER E
4.The function f is defined for all positive integers n by the following rule: f(n) is the number of positive integers each of which is less than n and has no positive factor in common with n other than 1. If p is any prime number, then f(p)=?
A.p-1 B.p-2 C.(p+1)/2 D.(p-1)/2 E.2
Answer:A
后天就考试了,题目还看不懂..晕死了~
拜托大家了!
The distribution of results of survay had a mean of 21hours and a standard deviation of 6. The number of hours of Pat(是一個人)watch tv last week was between 1 and 2 standard deviations below the mean. Pat上周可能看了多少小時的電視?
standard deviations is 6,mean is 21, 2 standard deviations below the mean is 21-2*6=9
啊谢谢,我现在算是明白 standard deviation的意思了...
4.The function f is defined for all positive integers n by the following rule: f(n) is the number of positive integers each of which is less than n and has no positive factor in common with n other than 1. If p is any prime number, then f(p)=?
对于函数f,被定义为:对于所有正整数n,f(n)是小于n的正整数的个数,这些正整数必须和n没有共同的正因子(1除外),如果p是质数,f(p)=?
质数只有2个因子,1和本身,比p小的正整数一共P-1个,这些数字不可能和p有公因子。
3. DS If 500 is the multiple of 100 that is closest to X and 400 is the multiple of 100 that is closest to Y, which multiple of 100 is closest to X+Y?
1)x<500
2) y<400
500是100的倍数中最靠近x的,450<X<550
400......................................Y..., 350<Y<450
800<x+y<1000 将2个条件代入800<X+Y<900,由于不知道和850的关系,所以无法确定最接近的是800还是900
I am not a NN, but try to help...
2. 70,75,80,85,90,105,105,130,130,130
The list shown consists of the times, in seconds, that it took each of 10 school children to run a distance of 400 meters. If the standard deviation of the 10 running times is 22.4 seconds, rounded to the nearest tenth of a second, how many of the 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
1. the mean of the 10 running times:
(70+75+80+85+90+105+105+130+130+130)/10=100
2. 1 standard deviation below:
below 100-22.5=77.5
3. 70, 75 are the times meets the requirement --> answer B
欢迎光临 ChaseDream (https://forum.chasedream.com/) | Powered by Discuz! X3.3 |