After having read what Subhotosh Khan asked you to read, let's deal with each question in a separate post. Let's devote this thread to #11.
[MATH]\text {P(A | B)} = \dfrac{\displaystyle \text {P(A and B)}}{\displaystyle \text {P(B)}}.[/MATH]
Have you ever seen that before? If so, what does it mean and what is its relevance to this problem?