a Can you draw a trend line? If so, which direction does it point as you move from left to right on the graph?
B
b Use two points to find the slope and to find a prediction equation.
C
c Find the value of y when x=2500.
A
aType of correlation: Weak negative.
Scatter plot and a line of fit:
B
b y=- 0.008x+22
C
c 2^(∘)C
Practice makes perfect
a When analyzing data using a scatter plot, there are three general outcomes: positive correlation, negative correlation, or no correlation.
Observation
Type of Correlation
As x increases, y increases.
Positive
As x increases, y decreases.
Negative
There is no visible pattern.
No
Observing the Graph
By treating the table as a set of points, we can graph the given data as a scatter plot. Do you see any trends?
It looks like there is some kind of correlation. Let's draw a line of fit, or trend line, to help us identify the type of correlation. To do so, we will draw a line through two points that appear to represent the data well, such as (0,22) and (2000,6).
As depth increases, temperature very slowly decreases. This indicates a weak negative correlation between temperature and depth.
b To write an equation for the line of fit we determined above, we first need to use two points on the line to find its slope. Let's use (0,22) and (2000,6) in the Slope Formula.
c To calculate the expected temperature at a given depth, we can substitute the value into our equation of fit. In this case, we will substitute the depth 2500 for x in our equation and solve for y.
