Math Word Problems Demystified - A Self Teaching Guide

The set of all possible outcomes of a probability experiment is called the

sample space. Each outcome in a sample space, unless otherwise noted, is

considered equally likely, that is, it has the same chance of occurring. An

eventcan consist of outcomes in the sample space. The basic definition of

probability of an event is

PðEÞ¼

Number of outcomes in eventE

Total number of outcomes in the sample space

The strategy when determining the probability of an event then is

1. Find the number of outcomes in eventE.


2. Find the number of outcomes in the sample space.


3. Divide the first number by the second number to get a decimal or
   reduce the fraction if a fraction answer is desired.

EXAMPLE:A die is rolled; find the probability of getting an odd number.

SOLUTION:

GOAL: You are being asked to find the probability of getting an odd

number.

STRATEGY: When a die is rolled, there are six outcomes in the sample

space, and there are three outcomes in the event. That is, there are three odd

numbers: 1, 3, and 5.

IMPLEMENTATION:P(odd number)¼

3

6

¼

1

2

or 0.5.

EVALUATION: Since 1, 3, and 5 are half of the numbers in the sample

space, the probability is correct.

When two coins are tossed, the sample space is

HH, HT, TH, TT

EXAMPLE:Two coins are tossed. Find the probability of getting a head and

a tail in any order.

SOLUTION:

GOAL: You are being asked to find the probability of getting a head and a

tail in any order.

268 LESSON 22 Word Problems in Probability