Page 22 - Probability Demystified

CHAPTER 1 Basic Concepts 11

8. There are 38 outcomes:

18 9
a. P(red) = ¼ .
38 19
2 1
b. P(green) = ¼ .
38 19
9. The sample space is 1c=,5c=, 10c=, 25c=, 50c=.
1
a. P(25c=) ¼ .
5
3
b. P(greater than 5c=) ¼ .
5
2
c. P(denomination ends in zero) ¼ .
5
10. The sample space consists of six women and three men.
3 1
PðmanÞ¼ ¼ :
9 3

Empirical Probability

Probabilities can be computed for situations that do not use sample spaces.
In such cases, frequency distributions are used and the probability is called
empirical probability. For example, suppose a class of students consists of
4 freshmen, 8 sophomores, 6 juniors, and 7 seniors. The information can be
summarized in a frequency distribution as follows:

Rank Frequency
Freshmen 4
Sophomores 8
Juniors 6
Seniors 7
TOTAL 25

From a frequency distribution, probabilities can be computed using the
following formula.