{X=0}与{X+Y=1}互相独立-->P({X=0}与{X+Y=1})=P({X=0})P({X+Y=1})--->P(X=0,Y=1)=P({X=0})P({X+Y=1})--->a=(0.4+b)*(a+b)又0.4+a+b+0.1=1--->a=0.3,b=0.2
