9-2
9-2 Experimental
ExperimentalProbability
Probability
Warm Up
Problem of the Day
Lesson Presentation
Pre-Algebra
Pre-Algebra
9-2 Experimental Probability
Warm Up
Use the table to find the probability of
each event.
1. A or B occurring 0.494
2. C not occurring 0.742
3. A, D, or E occurring
0.588
Pre-Algebra
9-2 Experimental Probability
Problem of the Day
A spinner has 4 colors: red, blue, yellow,
and green. The green and yellow
sections are equal in size. If the
probability of not spinning red or blue is
40%, what is the probability of spinning
green? 20%
Pre-Algebra
9-2 Experimental Probability
Learn to estimate probability using
experimental methods.
Pre-Algebra
9-2 Experimental Probability
Vocabulary
experimental probability
Pre-Algebra
9-2 Experimental Probability
In experimental probability, the likelihood
of an event is estimated by repeating an
experiment many times and observing the
number of times the event happens. That
number is divided by the total number of
trials. The more the experiment is repeated,
the more accurate the estimate is likely to
be.
probability 
Pre-Algebra
number of times the event occurs
total number of trials
9-2 Experimental Probability
Additional Example 1A: Estimating the Probability of
an Event
A. The table shows the results of 500 spins of
a spinner. Estimate the probability of the
spinner landing on 2.
probability  number of spins that landed on 2 = 186
total number of spins
500
The probability of landing on 2 is about 0.372, or 37.2%.
Pre-Algebra
9-2 Experimental Probability
Additional Example 1B: Estimating the Probability of
an Event
B. A customs officer at the New York–Canada
border noticed that of the 60 cars that he saw,
28 had New York license plates, 21 had
Canadian license plates, and 11 had other
license plates. Estimate the probability that a
car will have Canadian license plates.
probability  number of Canadian license plates
total number of license plates
= 21
60
= 0.35
The probability that a car will have Canadian license
plates is about 0.35, or 35%.
Pre-Algebra
9-2 Experimental Probability
Try This: Example 1A
A. Jeff tosses a quarter 1000 times and finds
that it lands heads 523 times. What is the
probability that the next toss will land
heads? Tails?
523
P(heads) = 1000= 0.523
P(heads) + P(tails) = 1
0.523 + P(tails) = 1
The probabilities must
equal 1.
P(tails) = 0.477
Pre-Algebra
9-2 Experimental Probability
Try This: Example 1B
B. Josie sells TVs. On Monday she sold 13
plasma displays and 37 tube TVs. What is the
probability that the first TV sold on Tuesday
will be a plasma display? A tube TV?
probability ≈ number of plasma displays = 13
= 13
total number of TVs
13 + 37 50
P(plasma) = 0.26
P(plasma) + P(tube) = 1
0.26
Pre-Algebra
+ P(tube) = 1
P(tube) = 0.74
9-2 Experimental Probability
Additional Example 2: Application
Use the table to compare the probability
that the Huskies will win their next game
with the probability that the Knights will
win their next game.
Pre-Algebra
9-2 Experimental Probability
Additional Example 2 Continued
probability 
number of wins
total number of games
probability for a Huskies win  79  0.572
138
probability for a Knights win  90  0.616
146
The Knights are more likely to win their next
game than the Huskies.
Pre-Algebra
9-2 Experimental Probability
Try This: Example 2
Use the table to compare the probability
that the Huskies will win their next game
with the probability that the Cougars will
win their next game.
Pre-Algebra
9-2 Experimental Probability
Try This: Example 2 Continued
probability 
number of wins
total number of games
probability for a Huskies win  79  0.572
138
probability for a Cougars win  85  0.567
150
The Huskies are more likely to win their next
game than the Cougars.
Pre-Algebra
9-2 Experimental Probability
Lesson Quiz: Part 1
1. Of 425, 234 seniors were enrolled in a math
course. Estimate the probability that a
randomly selected senior is enrolled in a
math course. 0.55, or 55%
2. Mason made a hit 34 out of his last 125
times at bat. Estimate the probability that he
will make a hit his next time at bat.
0.27, or 27%
Pre-Algebra
9-2 Experimental Probability
Lesson Quiz: Part 2
3. Christina polled 176 students about their
favorite ice cream flavor. 63 students’ favorite
flavor is vanilla and 40 students’ favorite
flavor is strawberry. Compare the probability
of a student’s liking vanilla to a student’s
liking strawberry.
about 36% to about 23%
Pre-Algebra