In this lesson, we learn how to find the probability 0f an event or either of two events.
-P(event A) = favorable outcomes/total # of outcomes
-P(A or B) = P(A) + P(B) - P(A & B)
-P(A or B) = P(A) + P(B) *mutually exclusive*
Example 1: A standard deck of cards consists of 52 cards, with 13 cards in each of four suits (clubs, spades, diamonds, and hearts). Clubs and spades are always black, while diamonds and hearts are always red. The face cards are the jacks, queens, and kings. If the deck is shuffled correctly, what is the probability that the top card is:
a) a red ace
=2/52 = 1/26
b) not a red ace
=50/52 = 25/26
c) a spade face card
=3/52
Example 2: One of the integers between 11 and 20, inclusive, is picked at random. What is the probability that the integer is:
a) even
= 1/2
b) divisible by 3
= 3/10
c) a prime
= 4/10 = 2/5
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