Box P has 2 red balls and 3 blue balls and Q has 3 red balls and 1 blue ball.
Let p:selection of box P ,q: selection of box Q ,r: Red ball being selected
P(p)=1/3 P(q)=2/3
P(r)=P(r|p)*P(p)+P(r|q)*P(q)=(2/5)*(1/3)+(3/4)*(2/3)=38/60
P(p|r)=P(p∩r)/P(r)=(P(r|p)*P(p))/(38/60)=(2/15)*(60/38)=4/19