Originally Posted by

**Chekhov** Hello, I have a few simple questions that I need help with. I have just started learning this.

1) A survey of 200 hundred teenagers showed that during the Christmas holidays, 120 watched cricket regularly, 85 watched tennis regularly and 60 were not regular viewers of either sport. What is the probability that a teenager selected at random from the group regularly watched:

a) both cricket and tennis

b) cricket but not tennis

c) at least on of the two sports

We are given this formula: P(AUB) = P(A) + P(B) - P(A^B) **where ^ is intersection).

How do I determine the intersection of A and B? Could someone please show me how to set these out in proper set notation?

Mr F says: I'd suggest you first try drawing a Venn diagram.

2) A box contains two red and five blue pens. Two pens are selected at random. What is the probability that the second pen is blue?

We are given the conditional formula: P(B|A) = P(A^B)/P(A)

Again, if someone could show me the steps for setting out in the notation it would be very much appreciated. I just need an example to get my head around.

Mr F says: I'd suggest you first try drawing a tree diagram.

Thanks.