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Chapter 10:
Counting Methods
10.1
Counting by Systematic Listing
• One-part tasks: each item in the list is
identified by one feature
• Multi-part tasks: items in the list are
identified by more than one feature (ex a
playing card has a suit and a value)
10.1
Two-part tasks: Using Tables
• Example: Determine the number of twodigit numbers that can be made using 2,4
and 7 for each digit
• Example: Determine how many ways you
can pick two people from the group of
Andria, Bridget, Connor and Dylan.
Uniformity Criterion
• A multi-part task is said to
satisfy the uniformity
criterion if the number of
choices for any particular part
is the same no matter which
choices were selected for
previous parts
10.2
10.2
Fundamental Counting Principle
(FCP)
• For a task that consists of k separate parts
and satisfies the uniformity criterion
• Suppose there are n1 ways to do the first
task, n2 ways to do the second, etc
• Then total number of ways to complete the
task is
n1 × n2 × … × nk
Example
10.2
Using the digits 0,1,2,3,4,5,6,7,8,9, how
many 4 digit numbers are there such that
a) 0 isn’t used for first, repetition is okay
b) 0 isn’t used for first, numbers all distinct
c) Number is odd and greater than 5000,
repetition is okay
10.2
Factorials and Arrangements
• n! = n × (n-1) × (n-2) × … 2 × 1
• 0! = 1
• The total number of different
ways to arrange n distinct
objects is n!
10.3
Permutations
Combinations
10.3
10.3
Guidelines for Choosing
Counting Method
• If selected items can be repeated or are
separate, use FCP
• If selected items cannot be repeated and
order is important, use permutations
• If selected items cannot be repeated and
order isn’t important, use combinations
Pascal’s Triangle
C(n,r) gives the number in the rth spot
of of the nth row
10.4
Counting and Gambling
• In a standard deck of cards, each card has
a suit (clubs, spades, hearts or diamonds)
and a rank (2,3,4,5,6,7,8,9,10, Jack,
Queen, King, Ace).
• There are 4×13 =52 cards in total
• A poker hand has 5 different cards from
the deck
Poker Hands
How many hands in
total? C(52,5)
How many four of a
kind?
How many
straights?
How many three of
a kind?