问题如下:
A discrete uniform distribution has the following outcomes for N: [7, 8, 9, 10]. what is the variance of this distribution ?
选项:
A. 1.00.
B. 1.25.
C. 3.00.
D. 3.25.
解释:
B is correct
考点:Expected Value & Variance
解析:因为离散均匀分布的每个值发生概率相同,所以7,8,9,10对应的概率都是25%:
先求期望:(0.25)(7+8+9+10)= 8.5
然后求方差:Variance = (0.25)[(7 -8.5)2 + (8 - 8.5)2 + (9 -8.5)2 + (10 - 8.5)2] = 1.25
为什么求方差的时候要乘以0.25?