Question

Barb pulled the plug in her bathtub and it started to drain. The amount of water in the bathtub as it drains is represented by the equation L = -5t - 8t + 120, where L represents the number of liters of water in the bathtub and t represents the amount of time, in minutes, since the plug was pulled. How many liters of water were in the bathtub when Barb pulled the plug? Show your reasoning. Determine, to the nearest tenth of a minute, the amount of time it takes for all the water in the bathtub to drain.

Answer 1

The bathtub had 120 L of water before Barb
pulled the plug.
It will take about 9.23 minutes for the water to
drain out.
Given equation: L=-5t - 8t + 120
Simplified: L=-13t + 120
Notice how it's written in slope-intercept form (y
= mx+b)
The y-intercept (L) is 120. So the coordinates for
L= (0, 120)
The coordinates mean that before the water in
the bathtub began draining out, it initially had
120 Liters of water.
Now that we know how many liters there were
before, the new equation would look like this: L
=-13t -> 120 = -13t
Solving the equation, we get that t=-9.23
minutes
Since time can't be negative, we'll just say that it
will take 9.23 minutes to drain out all the water.

Answer 2

The bathtub had 120 L of water before Barb pulled the plug.

It will take about 9.23 minutes for the water to drain out.

Given equation: L = -5t - 8t + 120

Simplified: L = -13t + 120

Notice how it's written in slope-intercept form (y = mx+b)

The y-intercept (L) is 120. So the coordinates for L = (0 , 120)

The coordinates mean that before the water in the bathtub began draining out, it initially had 120 Liters of water.

Now that we know how many liters there were before, the new equation would look like this: L = -13t --> 120 = -13t

Solving the equation, we get that t = -9.23 minutes

Since time can't be negative, we'll just say that it will take 9.23 minutes to drain out all the water.