Answer: The amount of salt in the tank after 8 minutes is 36.52 pounds.
Step-by-step explanation:
Salt in the tank is modelled by the Principle of Mass Conservation, which states:
(Salt mass rate per unit time to the tank) - (Salt mass per unit time from the tank) = (Salt accumulation rate of the tank)
Flow is measured as the product of salt concentration and flow. A well stirred mixture means that salt concentrations within tank and in the output mass flow are the same. Inflow salt concentration remains constant. Hence:
![c_{0} \cdot f_{in} - c(t) \cdot f_{out} = \frac{d(V_{tank}(t) \cdot c(t))}{dt}](https://tex.z-dn.net/?f=c_%7B0%7D%20%5Ccdot%20f_%7Bin%7D%20-%20c%28t%29%20%5Ccdot%20f_%7Bout%7D%20%3D%20%5Cfrac%7Bd%28V_%7Btank%7D%28t%29%20%5Ccdot%20c%28t%29%29%7D%7Bdt%7D)
By expanding the previous equation:
![c_{0} \cdot f_{in} - c(t) \cdot f_{out} = V_{tank}(t) \cdot \frac{dc(t)}{dt} + \frac{dV_{tank}(t)}{dt} \cdot c(t)](https://tex.z-dn.net/?f=c_%7B0%7D%20%5Ccdot%20f_%7Bin%7D%20-%20c%28t%29%20%5Ccdot%20f_%7Bout%7D%20%3D%20V_%7Btank%7D%28t%29%20%5Ccdot%20%5Cfrac%7Bdc%28t%29%7D%7Bdt%7D%20%2B%20%5Cfrac%7BdV_%7Btank%7D%28t%29%7D%7Bdt%7D%20%5Ccdot%20c%28t%29)
The tank capacity and capacity rate of change given in gallons and gallons per minute are, respectivelly:
![V_{tank} = 220\\\frac{dV_{tank}(t)}{dt} = 0](https://tex.z-dn.net/?f=V_%7Btank%7D%20%3D%20220%5C%5C%5Cfrac%7BdV_%7Btank%7D%28t%29%7D%7Bdt%7D%20%3D%200)
Since there is no accumulation within the tank, expression is simplified to this:
![c_{0} \cdot f_{in} - c(t) \cdot f_{out} = V_{tank}(t) \cdot \frac{dc(t)}{dt}](https://tex.z-dn.net/?f=c_%7B0%7D%20%5Ccdot%20f_%7Bin%7D%20-%20c%28t%29%20%5Ccdot%20f_%7Bout%7D%20%3D%20V_%7Btank%7D%28t%29%20%5Ccdot%20%5Cfrac%7Bdc%28t%29%7D%7Bdt%7D)
By rearranging the expression, it is noticed the presence of a First-Order Non-Homogeneous Linear Ordinary Differential Equation:
, where
.
![\frac{dc(t)}{dt} + \frac{f_{out}}{V_{tank}} \cdot c(t) = \frac{c_0}{V_{tank}} \cdot f_{in}](https://tex.z-dn.net/?f=%5Cfrac%7Bdc%28t%29%7D%7Bdt%7D%20%2B%20%5Cfrac%7Bf_%7Bout%7D%7D%7BV_%7Btank%7D%7D%20%5Ccdot%20c%28t%29%20%3D%20%5Cfrac%7Bc_0%7D%7BV_%7Btank%7D%7D%20%5Ccdot%20f_%7Bin%7D)
The solution of this equation is:
![c(t) = \frac{c_{0}}{f_{out}} \cdot ({1-e^{-\frac{f_{out}}{V_{tank}}\cdot t }})](https://tex.z-dn.net/?f=c%28t%29%20%3D%20%5Cfrac%7Bc_%7B0%7D%7D%7Bf_%7Bout%7D%7D%20%5Ccdot%20%28%7B1-e%5E%7B-%5Cfrac%7Bf_%7Bout%7D%7D%7BV_%7Btank%7D%7D%5Ccdot%20t%20%7D%7D%29)
The salt concentration after 8 minutes is:
![c(8) = 0.166 \frac{pounds}{gallon}](https://tex.z-dn.net/?f=c%288%29%20%3D%200.166%20%5Cfrac%7Bpounds%7D%7Bgallon%7D)
The instantaneous amount of salt in the tank is:
<h3>
Answer: Choice C</h3>
The largest exponent here is 4, so that makes it a quartic.
There are 3 terms, so we have a trinomial. Each term is separated by either a plus or a minus.
Choice A shows a quartic polynomial. Choice B is a cubic polynomial. Choice d is a quadratic trinomial.
Let's solve this by using the quadratic formula:
![\frac{-b+-\sqrt{b^2-4ac} }{2a}](https://tex.z-dn.net/?f=%5Cfrac%7B-b%2B-%5Csqrt%7Bb%5E2-4ac%7D%20%7D%7B2a%7D)
Note that we only use the coefficients so a=12, b=-14, and c=-6.
Plug values in the quadratic equation:
![\frac{ - ( - 14)± \sqrt{ {( - 14)}^{2} - 4(12)( - 6) } }{2(12)}](https://tex.z-dn.net/?f=%20%5Cfrac%7B%20-%20%20%28%20-%2014%29%C2%B1%20%5Csqrt%7B%20%7B%28%20-%2014%29%7D%5E%7B2%7D%20-%204%2812%29%28%20-%206%29%20%7D%20%7D%7B2%2812%29%7D%20)
And so by evaluating those values we obtain:
![\frac{14+-\sqrt{484} }{24}=\frac{14+-22}{24} \\\\](https://tex.z-dn.net/?f=%5Cfrac%7B14%2B-%5Csqrt%7B484%7D%20%7D%7B24%7D%3D%5Cfrac%7B14%2B-22%7D%7B24%7D%20%20%5C%5C%5C%5C)
Now we have two answers which are our factors one where we add another where we subtract and so:
First factor:
![\frac{14+22}{24}=\frac{36}{24}=\frac{3}{2}](https://tex.z-dn.net/?f=%5Cfrac%7B14%2B22%7D%7B24%7D%3D%5Cfrac%7B36%7D%7B24%7D%3D%5Cfrac%7B3%7D%7B2%7D)
Second Factor:
![\frac{14-22}{24}=\frac{-8}{24}=-\frac{1}{3}](https://tex.z-dn.net/?f=%5Cfrac%7B14-22%7D%7B24%7D%3D%5Cfrac%7B-8%7D%7B24%7D%3D-%5Cfrac%7B1%7D%7B3%7D)
And so your factors are
![\frac{3}{2},-\frac{1}{3}](https://tex.z-dn.net/?f=%5Cfrac%7B3%7D%7B2%7D%2C-%5Cfrac%7B1%7D%7B3%7D)
meaning that those are your roots/x-intercepts.
O would be the answer, but I’m not sure why you have 3
(360.00 to be exact)