# S1 Probabilities P(A' u B)

1. May 16, 2013

### Googl

Hi all,

Could you confirm this for me please. I am revising S1 statistics.

$$P(A' u B) = P(B) + P(A' u B')$$

Is that true?

I assume you can represent that on a venn diagram. Is that true.

I am having trouble understanding the equations which contain ' such as P(A' n B).

Thank you.

2. May 16, 2013

### mathman

The equation is correct, except for A'uB', which should be A'nB'.
If you want to make a Venn diagram, I suggest that you let C = A'.
CuB = B + CnB' (disjoint jets). You may be more comfortable using CnB' = C-B.