Example: A sample of 50 students could represent the population of the whole school
Example: If a sample of 50 students were needed, those students would need to be chosen at
random. A method like randomly drawing a few numbers from each class could work. Or
choose every fifth student that walks into the cafeteria.
Other Random Sample Methods:
 When there are 2 options to choose from: flip a coin
 When there are 6, 3, or 2 options to choose from: roll a die
(assign a number from 1-6 to each option, or 1 and 2 for one option, 3 and 4 for
another, and 5 and 6 for the last, evens for one option and odds for the other)
 Use calculator to generate random numbers (see example below)
Random samples cannot be biased. An example of a biased sample is only choosing
students that are in band to represent the population of the whole school.
Samples must be LARGE and RANDOM.
Example: Using a Calculator to Generate Random Numbers
Analyzing Samples:
We can compare samples to the population using percents. See the example below for an
example.
We can also set up proportions to solve random sample questions. See examples below.
Name: ________________________________
Date: ________________________
15.2 Random Samples-Homework
Circle the best answer choice.
1. For which situation could flipping a coin be sued to generate a random sample?
a. to predict student test scores
b. to predict the amount of money that a business will make in the next year
c. to predict the number of defective light bulbs in a sample
d. to predict which team will win a game
2. Which of the following describes a situation in which a data set with a low mean
absolute deviation is preferable?
(Hint: Remember, mean absolute deviation tells how spread out a data set is or how much it
varies.)
a. A car dealership sells cars at different prices
b. A factory manufactures computers of different sizes and shapes.
c. A food-processing plant fills each can with the same amount of soup.
d. A clothing store sells shirts in different sizes.
3. Charlie wants to randomly select one of three options for a new car. Which of the
following is one way he can do this?
a. Roll a number cube
b. Flip a coin
c. Flip a coin twice
d. Flip a coin and roll a number cube
4. For which situation could using a calculator to generate random numbers be
used to simulate a random sample?
a. to predict the number of defective cell phones in a shipment of 2000 phones
b. to choose between a red, blue, or black car
c. to predict the favorite subject of all the boys in a class
d. to predict the number of boys or girls born in a hospital in a year
(more on the back)
SHOW YOUR WORK for each of the following by using percents or a proportion. Simply
circling an answer will not get you ANY CREDIT.
5. A factory produced a batch of 200 light
bulbs, 20 of which are defective. The 20
defective light bulbs are labeled with the
integers 1 through 20. The other light bulbs
are labeled with the integers 21 through 200.
If you do a simulation of 50 random numbers
to predict the number of defective light
bulbs, how many numbers between 1 and
20 can you expect to generate?
a. 5
b. 10
c. 15
d. 20
A manufacturer ships a store 5000 MP3
players, of which 300 are defective. The store
manager does not know this but tests a
random sample of 10 players to look for
problems. A graphing calculator is used to
simulate the sample, with 1-300 representing
the defective players. The results are shown
in the table.
7. Complete the table to tell whether reach
number generated represents a good or
defective player.
8. From this sample, how many defective
players might the manager expect?
6. A random sample of 30 students were
asked to pick their favorite school subject
and 12 of them answered math. There
are 480 students in the school. How
many students in the school are likely to
pick math as their favorite subject.
a. 120 students
b. 192 students
c. 288 students
d. 360 students
Random
Number
13
2195
3873
525
900
167
1094
1472
709
5000
10.
Good or
Defective?
Find the mean absolute deviation of the
following data:
__________
28, 32, 47, 39, 38, 16, 40, 35, 54, 31
_____________
9. Is the manager’s expectation (your #8
answer) an accurate representation of
the whole shipment of MP3 players?
Explain.