【单选题】设随机变量X的概率密度为 ,k,a均大于0,且X的数学期望为0.75,则
【单选题】听力原文: The fiddler crab is a living clock. It indicates the time of the day by the color of its skin, which is dark by day and pale by night. The crab's changing skin color follows a regular twenty-fou...
A.
Why they change color.
B.
Whether they change color.
C.
How to use them as clocks.
D.
Where they can be caught.
【简答题】在某一大楼内,电梯的等候时间在[0,5]分钟之间均匀分布,则概率密度函数f(x)=______;等候时间大于0.5分钟的概率为______;电梯在最初45秒钟到达的概率为______;等候时间在1分钟至3分钟之间的概率为______.
【单选题】交换机是一种___________设备.
【简答题】的概率密度 , , 均大于0, 则 ____1(填“大于” “等于”或“小于”).