因为一月份与二月份被消费者投诉的次数互不影响,所以这两月的被投诉次数相互独立.即P(XY)=P(X)*P(Y),联合分布密度为
X=0 X=1 X=2
Y=0 0.4*0.4=0.16 0.5*0.4=0.2 0.1*0.4=0.04
Y=1 0.5*0.4=0.2 0.5*0.5=0.25 0.5*0.1=0.05
Y=2 0.1*0.4=0.04 0.1*0.5=0.05 0.1*0.1=0.01
P(X+Y=2)=P(X=0,Y=2)+P(X=1,Y=X)+P(X=2,Y=0)=0.04+0.25+0.04=0.33