Julissa is running a 10-kilometer race at a constant pace. After running for 18 minutes, she completes 2 kilometers. After running for 54 minutes, she completes 6 kilometers. Her trainer writes an equation letting [tex]$t$[/tex], the time in minutes, represent the independent variable and [tex]$k$[/tex], the number of kilometers, represent the dependent variable.

Which equation can be used to represent [tex]$k$[/tex], the number of kilometers Julissa runs in [tex]$t$[/tex] minutes?

A. [tex]$k - 2 = \frac{1}{9}(t - 18)$[/tex]
B. [tex]$k - 18 = \frac{1}{9}(t - 2)$[/tex]
C. [tex]$k - 2 = 9(t - 18)$[/tex]
D. [tex]$k - 18 = 9(t - 2)$[/tex]



Answer :

Given the data points, we need to determine the correct equation to represent the number of kilometers [tex]\( k \)[/tex] Julissa runs in [tex]\( t \)[/tex] minutes.

We know the following:
- After 18 minutes, Julissa has run 2 kilometers.
- After 54 minutes, Julissa has run 6 kilometers.

First, let's determine the rate at which she is running. The formula for the rate (slope) is:
[tex]\[ \text{slope} = \frac{\Delta k}{\Delta t} = \frac{k_2 - k_1}{t_2 - t_1} \][/tex]
Plugging in the given values:
[tex]\[ \text{slope} = \frac{6 - 2}{54 - 18} = \frac{4}{36} = \frac{1}{9} \][/tex]

Now, using the point-slope form of the equation of a line, which is:
[tex]\[ k - k_1 = \text{slope} \times (t - t_1) \][/tex]
We can choose either of the points [tex]\((18, 2)\)[/tex] or [tex]\((54, 6)\)[/tex]. Let's use [tex]\((18, 2)\)[/tex] to derive the equation:
[tex]\[ k - 2 = \frac{1}{9} \times (t - 18) \][/tex]

Thus, the equation that represents [tex]\( k \)[/tex] is:
[tex]\[ k - 2 = \frac{1}{9}(t - 18) \][/tex]

Therefore, the correct equation is:
[tex]\[ k - 2 = \frac{1}{9}(t - 18) \][/tex]