Math 141h-copyright Joe Kahlig, 10C
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Section 7.4: Use of Counting Techniques in Probability
Example: A type of license plate has three letters followed by two digits. If one of these plates is select
at random, find the probability that the letters are selected from the set {a, b, c, d, e}, the digit zero
is not used and no letter is repeated.
Example: A box contains 10 red, 8 green, and 5 black balls. What is the probability that in a sample
of 7 that exactly three red and at least 2 green balls were chosen?
Example: A standard deck of cards is shuffled and then 5 cards are dealt.
A) What is the probability of getting at least 1 heart?
B) What is the probability of the cards being all one suit?
C) What is the probability of getting a full house?
D) what is the probability of getting two pairs?
Math 141h-copyright Joe Kahlig, 10C
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Example: A 6 sided die is rolled 5 times. What is the probability that exactly 3 of the rolls are a 4.
Example: Find the probability that in a group of 6 people that all were born on a different days of
the year.
Example: Find the probability that at least two people in a group of 6 were born on the same day.
Example: Find the probability that in a group of 15 people, that at least two people were born in the
same month. Assume that months are equally likely.