1
Chapter (4) : Basic Probability (Examples)
Example (1):
A box contain five red balls, a ball is drawn at random, what is the
possibility that the ball will be red?
55 ST
1
5
5 S
T
RP
(Certain event)
Example (2):
A box contain five red balls, a ball is drawn at random, what is the
possibility that the ball will be blue?
50 ST
0
5
0 S
T
BP
(Impossible event)
Example (3):
An experiment is consisting of tossing (flip) a fair coin once, what is the
probability of getting a head?
S={ H,T} S= 2 n(H)= 1
50.0
2
1 S
T
HP
Example (4):
If an experiment is consisting of tossing a fair coin twice, find:
1. The Set of all possible outcomes of the experiment.
2. The probability of the event of getting at least one head.
3. The probability of the event of getting exactly one head in the two
tosses.
4. The probability of the event of getting two heads.
Solution:
1.
S= {HH, HT, TH, TT} Where,
And since the coin is fair, then all of the elementary events are equally
likely, i.e.
P(HH) = P(HT) = P(TH) = P(TT) = 0.25
2.
Let
E1 = {HH, HT, TH} be the event of getting at least one head, then
n(E1)=T =3
And hence
75.0
4
3
1 S
T
EP
3.
E2 = {HT, TH} be the event of getting exactly one head, then
n (E2) =2 And hence
2
T
