AFDA – Unit 9: Statistics and Surveys
Day 1 Notes: Measures of Central Tendency
and Normal Distribution
Name: _________________
Block: _____ Date:_______
Today…
 You will review the Measures of Central Tendency and Normal Distribution
 You will learn when to use which Measure of Central Tendency
The term “Measures of Central Tendency” refers to the three measures: Mean,
Median, and Mode.
Mean- _____________________________; the sum of a set of data divided by the
number of data.
Median- the __________________________ value, or the mean of the middle two
values, when the data is arranged in _______________________ order.
Mode- the data value that appears the ____________________.
You can have:



Practice #1: On a recent test, students of a math class earned the grades shown
below. Calculate the mean, median, and mode of the class.
65, 70, 72, 75, 77, 82, 84, 84, 84, 84, 86, 89, 89, 90, 92, 95, 97
Mean:
Median:
Mode:
Practice #2: Suppose there were two students absent on test day and they never
came to make up the test. How does that affect the measures of central tendency?
When do I use which?!
Use ______________________ when there is no outlier.
Use ______________________ when there is an outlier.
Normal Distribution:
The graph of a normal distribution is also
called a _______________________.
The data is symmetrical, or nearly so, around
the mean. The mean, median and mode are
almost (if not) identical.
Other Key Properties:
 The highest point occurs at _____________
 The area under the curve is _____________
 The area under the curve to the right of µ equals the area under the curve to the
left of µ which equals ½ or 50%.
 A normal curve is used to model or represent a corresponding normal
distribution.
The 68-95-99.7 (Empirical) Rule
In a normal model:
 about 68% of the values fall within one standard deviation of the mean
 about 95% of the values fall within two standard deviations of the mean
 about 99.7% (almost all!) fall within three standard deviations of the mean
Practice #3: Represent each of the following distributions on the normal distribution
graphs provided. For each, show three standard deviations to the left and three
standard deviations to the right of the mean.
a.) A normal distribution with a mean of 7 and a standard deviation of 2.
b.) The weights of cattle at the fair this year were normally distributed with a mean of
800 lbs. and a standard deviation of 65 lbs.
Practice #4: The braking distance for a Krazy-Car traveling at 50 mph is normally
distributed with a mean of 50 feet and a standard deviation of 5 feet. Answer the
following without using a calculator.
a.) What is the likelihood a Krazy-Car will take more than 65 feet to stop?
b.) What is the probability a Krazy-Car will stop between 45 feet and 55
feet?
c.) What percent of the time will a Krazy-Car traveling at 50 mph stop
between 35 feet and 55 feet?
d.) What is the probability a Krazy-Car will require less than 50 feet or
more than 60 feet to stop?