Mutually Exclusive Events
 Two events A and B are mutually exclusive if A and B
cannot happen at the same time.
 Event A: Roll a 3 on a die.
 Event B: Roll a 4 on a die.

Mutually Exclusive
 Event A: Roll a 3 on a die.
 Event B: Roll an odd number on a die.

Not Mutually Exclusive
Mutually Exclusive Events
 Event A – Randomly select a blood donor with type O
blood.
 Event B – Randomly select a female blood donor.
 Not Mutually Exclusive
 Event A – Randomly select a Ford truck.
 Event B – Randomly select a Chevy truck.
 Mutually Exclusive
The Addition Rule
 The probability that events A or B will occur P (A or B)
is given by P(A or B) = P(A) + P(B) – P(A and B)
 If events A and B are mutually exclusive, the rule can
be simplified to P(A or B) = P(A) + P(B).
The Addition Rule
 You select a card from a standard deck (52). Find the
probability of selecting a 4 or an ace:
 P (4 or ace) = P(4) + P(ace) = 4/52 + 4/52 = 8/52 ~0.152
 You roll a die. Find the probability of rolling a number
less than 3 or rolling an odd number:
 P (less than 3 or odd) = P(less than 3) + P(odd) – P(less
than 3 and odd)
 =2/6 + 3/6 – 1/6 = 4/6 ~ 0.67
Group Work
 White Book: Page 145-147…#9-14, 17-20.