Transcript Section 1.9

Trip Lenahan
Mr. Pricci
Honors Geometry, Mod 8
30 May 2008
Jobs That Use Probability
► Insurance
companies
► Professional card players
► Casino operators
► Athletes
► Sports Analysts
► Statistics keepers
► Secretaries
► Accountants
► Doctors
What is Probability?
► Probability
is the likelihood of something
happening.
► Probability is expressed as a fraction as the
number of desired outcomes over the
number of possible outcomes.
Two-Step Procedure
To determine probability, one may use this
two-step procedure:
1. Determine and count all logical
possibilities
2. Determine and count all desired
possibilities or “winners”
Probability Formula
The Probability Formula is as follows:
Probability= number of winners
number of possibilities
Example of Probability #1
► If
there are 10 balls (7 red, 3 blue) then the
likelihood of selecting a red ball on one attempt
is 7/10.
7
10
red balls (winners)
total balls (total possibilities)
Example of Probability #2
Problem: If one of the four points is picked
randomly, what is the probability that the point lies
on the angle?
Example of Probability #2 (cntd)
► To
solve this problem, we first list all
possibilities
A
B
C
D
► Then, we circle the winners
A
B
C
D
Example of Probability #2 Solution
Therefore the probability of the selected point
being on the angle is:
Winners
Possibilities
=
3
4
Practice Problem #1
If one of the four angles is selected
randomly, what is the probability that the
angle is acute?
Practice Problem #1 Solution
50
60
90
Probability= 2 = 1
4
2
130
Practice Problem #2
If two points are selected randomly, what
is the probability that both points are
greater than 10, but less than 15?
Practice Problem #2 Solution
AB
AC
AD
AE
AF
AG
AH
AI
BC
BD
BE
BF
BG
BH
BI
CD
CE
CF
CG
CH
CI
DE
DF
DG
DH
DI
EF
EG
EH
EI
FG
FH
FI
GH HI
GI
Probability= 6 = 1
36
6
Works Cited
Probability. 1 January 1999. Math Goodies Online.
28 May 2008.
<http://www.mathgoodies.com/lessons/vol6/intr
o_probability.html>.
Reed, Richard et al. Geometry; For Enjoyment and
Challenge. Evanston, Illinois. 1991.