1. LSP 120: Quantitative Reasoning and Technological Literacy Section 202
Özlem Elgün

3. Why are we here? Data: numbers with a context
Cell: each data point is recorded in a cell
Observation: each row of cells form an observation for a subject/individual
Variable: any characteristic of an individual

4. Why Data? 1) Data beat anecdotes
“Belief is no substitute for arithmetic.”
Henry Spencer
Data are more reliable than anecdotes, because they systematically describe an overall picture rather than focus on a few incidents .

5. Why Data?
2. Where the data come from is important. “Figures won’t lie, but liars will figure.” Gen. Charles H. Grosvenor ( ), Ohio Rep.

6. Familiarizing with Data
Open Excel
Collect data:
Ask 5 classmates the approximate # of text messages they send per day
Record the data on Excel spreadsheet
Calculate average using the Average function on Excel. (There are many functions such as sum, count, slope, intercept etc. that we will use in this class)

7. What is a linear function?
Most people would say it is a straight line or that it fits the equation y = mx + b. 
What is the relationship between the variables in a linear function? 
A linear function indicates a relationship between x and y that has a fixed or constant rate of change. 

8. Is the relationship between x and y is linear?
The first thing we want to do is be able to determine whether a table of values for 2 variables represents a linear function:

9. To determine if a relationship is linear in Excel, add a column in which you calculate the rate of change.
You must translate the definition of “change in y over change is x” to a formula using cell references. A B C 1 x y
Rate of Change 2 3 11 5 16
=(B3-B2)/(A3-A2) 4 7 21 9 26 6 31
This is a cell reference

10. If the rate of change values are constant then the relationship is a linear function. 
So this example does represent a linear function.  Rate of change is 2.5 and it is constant.
This means that that when the x value increases by 1, the y value increases by 2.5.  A B C 1 x y
Rate of Change 2 3 11 5 16
2.5 4 7 21 9 26 6 31

11. How to Write a Linear Equation
Next step is to write the equation for this function. 
y = mx + b. 
y and x are the variables 
m is the slope (rate of change)
b is the y-intercept (the initial value when x=0)
We know x, y, and m, we need to calculate b:
Using the first set of values (x=3 and y=11) and 2.5 for "m“ (slope):
11=2.5*3 + b. 
Solving:  11=7.5 + b
3.5 = b. 
The equation for this function is : y = 2.5 x + 3.5
Another way to find the equation is to use Excel’s intercept function.  A B C 1 x y
Rate of Change 2 3 11 5 16
2.5 4 7 21 9 26 6 31

12. Practice On the Class Website Open Rate of Change Calculations determine whether the function is linear and if so, write the equation for the function.  x y 5 -4 10 -1 15 2 20 x y 1 2 3 5 9 7 18 x y 2 20 4 13 6 8 -1

13. "Real world" example of a linear function:
Studies of the metabolism of alcohol consistently show that  blood alcohol content (BAC), after rising rapidly after ingesting alcohol, declines linearly.  For example, in one study, BAC in a fasting person rose to about %  after a single drink.  After an hour the level had dropped to %.  Assuming that BAC continues to decline linearly (meaning at a constant rate of change), approximately when will BAC drop to 0.002%?
In order to answer the question, you must express the relationship as an equation and then use to equation.  First, define the variables in the function and create a table in excel.
The two variables are time and BAC. 
Calculate the rate of change. 
Time
BAC
0.018% 1
0.010%

14. Therefore the BAC will reach .002% after 2 hours.
This rate of change means when the time increases by 1, the BAC decreases (since rate of change is negative) by .008.  In other words, the BAC % is decreasing .008 every hour.  Since we are told that BAC declines linearly, we can assume that figure stays constant.  Now write the equation with Y representing BAC and X the time in hours.  Y = -.008x
This equation can be used to make predictions.  The question is "when will the BAC reach .002%?"  Plug in .002 for Y and solve for X.
.002 = -.008x
-.016 = -.008x
x = 2
Therefore the BAC will reach .002% after 2 hours.
Time
BAC
Rate of change
0.018% 1
0.010%
-0.008%

15. Warning:  Not all graphs that look like lines represent linear functions
The graph of a linear function is a line.  However, a graph of a function can look like a line even thought the function is not linear.  Graph the following data where t is years and P is the population of Mexico (in millions):
What does the graph look like?
Now, calculate the rate of change
for each set of data points
(as we learned under
Does the data represent a
linear function?)  Is it constant? t P
1980
67.38
1981
69.13
1982
70.93
1983
72.77
1984
74.67
1985
76.61
1986
78.60

16. Does this data (derived from the same equation as the table
What if you were given the population for every ten years?  Would the graph no longer appear to be linear?  Graph the following data.
Does this data (derived from
the same equation as the table
above) appear to be linear? 
Both of these tables represent
an exponential model (which we
will be discussing shortly). 
The important thing to note is that
exponential data can appear to be
linear depending on how many data
points are graphed.  The only way to
determine if a data set is linear is to
calculate the rate of change (slope)
and verify that it is constant. t P
1980
67.38
1990
87.10
2000
112.58
2010
145.53
2020
188.12
2030
243.16
2040
314.32