Lesson 70- The event A or B

Addition Law:
a) General  Case:
               P (A or B) = P(A) + P(B) - P(A and B)                * Overlap
b) Special Sub-case:  
 If A and B are mutually exclusive then
    P(A and B) = P(A) + P(B)

Example 1:
One card is randomly drawn from deck of 52 cards
Define the following events:

S:  The card is a spade
R:  The card is red
F:  The card is face card

Which of these three are mutually exclusive?
S, R (do not overlap)

Determine the following probabilities directly by counting outcomes:
P(s) = 13/52   P(r)= 26/52    P(s and r)= O    P(s or r)= 13/52 + 26/52 = 39/52
P(s) = 13/52   P(f) = 12/52   P(s and f) = 3/52   P(s or f) = 13/52 + 12/52 - 3/52 = 22/52

*note: using a Venn-diagram with these problems will make things a lot easier, as the info. is right in front of you.