MATH 103 Unit 8 Summary
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MATH 103 Unit 8 Summary
2022
Unit 8
8.1 Counting Principles and Probability
The (Extended) Fundamental Counting Principle
If a first action can be performed in a ways, a second action in b ways, a third in c ways, . . . , and so on, then all of the actions can be performed together, in this order, in a × b × c × · · · ways.
Basic Methods of Counting
Method 1: Tree diagram
Method 2: Blanks, squares, boxes, etc.
Definition: Permutation
A permutation is an ordered arrangement of elements from a given set.
For example, the permutations of the letters A, B , C, and D taken two distinct letters at a time are
AB AC AD
BA BC BD
CA CB CD
DA DB DC
Note that the order matters, so AB and BA are different arrangements.
Definition: Combination
A Combination is an unordered selection of items taken from a given set.
For example, the combinations of the letters A, B , C, and D taken two distinct letters at a time are
AB AC AD BC BD CD
8.2 Permutations – Ordered Arrangements
Theorem
The number of ways to arrange n distinct objects in order is n!. Said another way, n Pn = n!. The number of permutations of an n distinct element set is n!.
Note: 0! = 1
Permutations Summary
• If n objects are distinct, there are n! permutations of the objects. That is to say, there are n! ways of arranging them.
• If r objects are arranged from a group of n distinct objects there are n Pr permutations of the objects. That is to say there are n Pr ways of arranging the r objects, and
n!
n Pr = P(n,r) =
• If a collection of n elements is to be arranged and a elements are indistinguishable of one type, b elements are indistinguishable of a second type, c elements are indistinguishable of a third type, and so on, then the number of arrangements is
n!
a!b!c! ···
The Birthday Problem
P(at least two people in a group of k people will share a birthday) = 1 −
8.3 Combinations – Unordered Selections
The Number of Combinations Formula
The total number of combinations of n objects taken r at a time is equal to
n Cr = r(n) =
8.4 Binomial Models
A portion of the Pascal’s triangle is shown below. For example, 3(4) is in row n = 4 and in
position r = 3.
Theorem: Binomial Theorem
If n is a natural number, then the binomial expansion of (x + y)n is given by
(x + y)n = 0 xn + 1 xn − 1y + 2 xn −2y2 + ··· + r xn −r yr + ··· + n yn
Written in sigma notation:
(x + y)n = k xn −k yk = k xk yn −k
Example: In the expansion of (2x − 3)9 , determine the coefficient of term containing x3 .
Solution: The general term of the expansion of (a + b)n is r(n) an −r br .
Using a = 2x, b = −3, and n = 9:
r(n) an −r br = r(9) (2x)9 −r ( −3)r
= r(9) (2)9 −r ( −3)r x9 −r
For the term containing x3 , we require 9 − r = 3:
9 − r = 3
r = 6
Therefore,
r(9) (2)9 −r ( −3)r x9 −r = 6(9) (2)9 −6 ( −3)6 x9 −6
= (84)(8)(729)x3
= 489888x3
Therefore, the coefficient of term containing x3 is 489888.
A binomial experiment is a probability experiment that satisfies all of the following four requirements.
• The number of trials, called Bernoulli trials, is fixed;
• Each trial is independent of the other trials;
• There are only two outcomes (sometimes referred to as success or failure) with each trial; and
• The probability of each outcome remains constant from trial to trial.
As an example, tossing a coin five times and recording the number of heads is a binomial experiment.
• There are five trials.
• The coin has no ”memory,” so each flip of the coin is independent of the others.
• There are only two outcomes, heads or tails (with heads defined as a success).
• The probability of a head remains at for every trial.
The binomial distribution is a discrete probability distribution of the number of successes in a series of n independent trials with each trial having two possible outcomes and a con- stant probability of success.
Definition: Binomial Distribution
In general, the binomial distribution is given by
P(X = x) = x(n) px qn −x or P(X = x) = x(n) px (1 − p)n −x
where
• p is the numerical probability of a defined success,
• q is the numerical probability of a defined failure,
• n is the number of trials,
• x is the number of success in n trials, and
• X is the assigned random variable.
The expectation of the number of successes in a binomial distribution of n Bernoulli trials with probability p of success on each trial is
E(X) = np
Example: A manufacturing company that makes a specific car component estimates that 0.1% of their products are defective. If a customer orders 25 of the components, what is the probability that at least one of the components is defective?
Solution: P(at least one is defective) = 1 − P(X = 0) = 1 − 0(25) (0.001)0 (0.999)25 ≈ 0.025
Definition: Hypergeometric Distribution
In general, the hypergeometric distribution is given by
x(s) ×
n
• m(n) equals the number of subsets of size m, selected from the whole group of n;
• x(s) equals the number of subsets of size x, selected from the set of successes s, and
• equals the number of subsets of size m − x, selected from the set of n − s failures.
The formula to compute the expected number of successes in a hypergeometric distri-
bution of n trials is
2022-04-13