题目
An analyst has determined that the probability that the S&P 500 index will increase on any given day is 0.60 and the probability that it will decrease is 0.40. The expected value and variance of the number of up days in a 5-day period are closest to:
选项
A.3.0 and 1.2
B.3.0 and 1.1
C.2.0 and 0.5
D.2.0 and 2.1
答案
A
解析
E(X)=np=5×0.6=3.0,V(X)=npq=5×0.6×0.4=1.2,E(X)=np=5×0.6=3.0, V(X)=npq=5×0.6×0.4=1.2