Counting and Probability

Imagine tossing two coins and observing whether 0, 1, or 2 heads are obtained. Below are the results after 50 tosses

Tossing Two Coins

Set of possible outcome of tossing two coins

Outcomes for 2 heads

Outcomes for 1 head

Outcomes for 0 heads

In case an experiment has finitely many outcomes and all outcomes are equally

likely to occur, the probability of an event (set of outcomes) is just the ratio of the

number of outcomes in the event to the total number of outcomes (sample space).

NOTATION For a finite set A, the number of elements of A is denoted N(A) or |A|

Probabilities Tossing Two Coins

Outcomes for 2 heads

Outcomes for 1 head

Rolling A Pair of DiceA die is one of a pair of dice. Suppose a blue die and a gray die are rolled together, and the numbers of dots that occur face up on each are recorded.The possible outcomes can be listed as follows, where in each case the die on the left is blue and the one on the right is gray.

NOTATIONThe outcome can be represented as (2,4) or 24 The outcome can be represented as (5,3) or 53With this notation the set of all possible outcomes can be represented as

What is the probability that the sum of the outcome is 5?

What is the probability that outcome is an even numbers?

Counting Consecutive Integers

Determine the size of each of the following sets{0, 1, 2, …., n}

{3, 4, 5, …., 100}

{3+0,3+1,…,3+(100-3)}

{37,38,39,….,10278}

{37+0,37+1,…,37+(10278-37)}

What is the size of the set of integers

{n, n+1, n+2,…., m} ?

Application of Counting a Lista. How many three-digit integers (integers

from 100 to 999 inclusive) are divisible by 5?

(Describe that set as a list)

b. What is the probability that a randomly chosen three-digit integer is divisible by 5?