Jefferson Middle School Group Fraction of the Population 6th grade 7th grade 8th grade boys girls Example 2 STANDARDIZED TEST

Document Sample
Jefferson Middle School Group Fraction of the Population 6th grade 7th grade 8th grade boys girls Example 2 STANDARDIZED TEST Powered By Docstoc
					Lesson 8-4

Example 1 Probability of Independent Events
The two spinners are spun. What is the
probability that both spinners will show an odd
number?

                          1
P(first spinner is odd) = 2
                           4
P(second spinner is odd) = 7
                           1 4 2
P(both spinners are odd) = 2 · 7 or 7



Example 2 STANDARDIZED TEST PRACTICE                                 Jefferson Middle School
EXAMPLE                                                                            Fraction
Use the information in the table at the right. What is the        Group
                                                                              of the Population
probability that a student picked at random will be an                                 2
eighth grade girl?                                                6th grade
                                                                                       9
    1             3            1               2                                       4
A             B              C              D                     7th grade
   10            10            3               5                                       9
                                                                                       1
Read the Test Item                                                8th grade
                                                                                       3
You are asked to find the probability that a student picked at                         7
random will be an eighth grader and a girl. The events are        boys
                                                                                      10
independent because the grade of the student does not                                  3
determine the gender.                                             girls
                                                                                      10
Solve the Test Item
First, find the probability of each event.
                 1
P(8th grade) = 3
           3
P(girl) = 10
Then, find the probability of both events occurring.
                          1 3       1
P(8th grade and girl) = 3 · 10 or 10
                                                  1
The probability that the two events will occur is , which is A.
                                                 10
Example 3 Probability of Dependent Events
There are 3 red, 6 blue, and 11 green marbles in a bag. Once a marble is selected, it is not
replaced. Find the probability that 2 red marbles are chosen.

Since the first marble is not replaced, the first event affects the second event. These are
dependent events.
                          3  number of red marbles
P(first marble is red) = 20
                               total number of marbles

                           2  number of red marbles after one red marble is removed
P(second marble is red) = 19
                              total number of marbles after one red marble is removed

                             1
                     3 2        3
P(two red marbles) =    or
                     20 19 190
                        10

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:2
posted:10/4/2012
language:English
pages:2