Describing a Real-World Linear Equation

A tub filled with 50 quarts of water empties at a rate of 2.5 quarts per minute. Let [tex][tex]$w=$[/tex][/tex] quarts of water left in the tub and [tex][tex]$t=$[/tex][/tex] time in minutes.

[tex]\[
\begin{tabular}{|c|c|}
\hline
Time [tex]$( t )$[/tex] & Quarts of water [tex]$( w )$[/tex] \\
\hline
0 & 50 \\
\hline
2 & 45 \\
\hline
4 & 40 \\
\hline
\end{tabular}
\][/tex]

Choose the correct answers.

Which equation models the relationship?
[tex]\[
\begin{array}{l}
\text{A. } t = 2.5 - 50 w \\
\text{B. } t = 50 - 2.5 w \\
\text{C. } w = 2.5 - 50 t \\
\text{D. } w = 50 - 2.5 t
\end{array}
\][/tex]



Answer :

Let's determine which equation models the relationship between the time [tex]\( t \)[/tex] in minutes and the quarts of water [tex]\( w \)[/tex] left in the tub.

From the problem, we know the following:

- The tub initially has 50 quarts of water.
- The tub empties at a rate of 2.5 quarts per minute.

We can use these pieces of information to form a linear equation.

When [tex]\( t = 0 \)[/tex], the initial amount of water [tex]\( w \)[/tex] is 50 quarts. Therefore, we start with the point (0, 50).

For every minute that passes, the water decreases by 2.5 quarts. This tells us the water [tex]\( w \)[/tex] will be impacted by the rate over time.

A linear relationship can be expressed as:
[tex]\[ w = w_{initial} - (rate \times t) \][/tex]

Substituting the given values:
[tex]\[ w = 50 - 2.5t \][/tex]

This equation [tex]\( w = 50 - 2.5t \)[/tex] correctly models the situation.

To find the solution when [tex]\( t = 30 \)[/tex] minutes, we can substitute [tex]\( t \)[/tex] with 30 into our equation:
[tex]\[ w = 50 - 2.5t \][/tex]

Substituting [tex]\( t = 30 \)[/tex]:
[tex]\[ w = 50 - 2.5 \times 30 \][/tex]

[tex]\[ w = 50 - 75 \][/tex]

[tex]\[ w = -25 \][/tex]

Therefore, when [tex]\( t = 30 \)[/tex] minutes, the amount of water left in the tub is [tex]\( -25 \)[/tex] quarts.

So, the correct equation that models the relationship is:
[tex]\[ w = 50 - 2.5t \][/tex]

The solution when the time is 30 minutes is:
[tex]\[ w = -25 \text{ quarts} \][/tex]