Page 15 - Probability Demystified

4 CHAPTER 1 Basic Concepts

EXAMPLE: Two coins are tossed; find the probability that both coins land
heads up.

SOLUTION:

The sample space for tossing two coins is HH, HT, TH, and TT. Since there
are 4 events in the sample space, and only one way to get two heads (HH),
the answer is

1
PðHHÞ¼
4

EXAMPLE: A die is tossed; find the probability of each event:

a. Getting a two
b. Getting an even number

c. Getting a number less than 5

SOLUTION:

The sample space is 1, 2, 3, 4, 5, 6, so there are six outcomes in the sample
space.
1
a. P(2) ¼ , since there is only one way to obtain a 2.
6
3 1
b. P(even number) ¼ ¼ , since there are three ways to get an odd
6 2
number, 1, 3, or 5.
4 2
c. P(number less than 5Þ¼ ¼ , since there are four numbers in the
6 3
sample space less than 5.

EXAMPLE: A dish contains 8 red jellybeans, 5 yellow jellybeans, 3 black
jellybeans, and 4 pink jellybeans. If a jellybean is selected at random, find the
probability that it is
a. A red jellybean
b. A black or pink jellybean

c. Not yellow
d. An orange jellybean