A white ball can be drawn in two mutually exclusive ways:
(I) By transferring a black ball from first to second bag, then drawing a white ball
(II) By transferring a white ball from first to second bag, then drawing a white ball
Let E1, E2 and A be the events as defined below:
E1 = A black ball is transferred from first to second bag
E2 = A white ball is transferred from first to second bag
A = A white ball is drawn