A graph titled Monthly Sales and Advertising Costs has Advertising Costs (1,000 dollars) on the x-axis and sales (1,000 dollars) on the y-axis. A line goes through points (6.4, 117) and (6.6, 120).

Question

The scatterplot and trend line show a positive correlation between advertising costs and sales.

Using the points (6.4, 117) and (6.6, 120), what is the slope of the trend line?
–15
–12
12
15

Answer 1

To find the slope of the trend line that passes through the points $(6.4,117)$ and $(6.6,120)$, we use the formula for the slope $m$ of a line, which is defined as:

$$m=\frac{y_2-y_1}{x_2-x_1}$$

Here, we can assign the points as follows:

• $(x_1,y_1)=(6.4,117)$
• $(x_2,y_2)=(6.6,120)$

Now we can substitute the values into the formula:

$$m=\frac{120-117}{6.6-6.4}=\frac{3}{0.2}=15$$

Thus, the slope of the trend line is 15.