Answer:
Kyle filled 4 10-oz cups, 6 14-oz cups, and 4 20-oz cups.
Step-by-step explanation:
Let 10-oz, 14-oz, and 20-oz coffees be represented by the variables <em>a, b</em>, and <em>c</em>, respectively.
Since a total of 14 cups of coffee was served:
![a+b+c=14](https://tex.z-dn.net/?f=a%2Bb%2Bc%3D14)
A total of 204 ounces of coffee was served. Therefore:
![10a+14b+20c=204](https://tex.z-dn.net/?f=10a%2B14b%2B20c%3D204)
A total of $16.70 was collected. Hence:
![0.95a+1.15b+1.5c=16.7](https://tex.z-dn.net/?f=0.95a%2B1.15b%2B1.5c%3D16.7)
This yields a triple system of equations. In order to solve a triple system, we should isolate the system to only two variables first.
From the first equation, let's subtract <em>a</em> and <em>b</em> from both sides:
![c=14-a-b](https://tex.z-dn.net/?f=c%3D14-a-b)
Substitute this into both the second and third equations:
![10a+14b+20(14-a-b)=204](https://tex.z-dn.net/?f=10a%2B14b%2B20%2814-a-b%29%3D204)
And:
![0.95a+1.15b+1.5(14-a-b)=16.7](https://tex.z-dn.net/?f=0.95a%2B1.15b%2B1.5%2814-a-b%29%3D16.7)
In this way, we've successfully created a system of two equations, which can be more easily solved. Distribute:
For the Second Equation:
![\displaystyle \begin{aligned} 10a+14b+280-20a-20b&=204\\ -10a-6b&=-76\\5a+3b&=38\end{aligned}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cbegin%7Baligned%7D%2010a%2B14b%2B280-20a-20b%26%3D204%5C%5C%20-10a-6b%26%3D-76%5C%5C5a%2B3b%26%3D38%5Cend%7Baligned%7D)
And for the Third:
![\displaystyle \begin{aligned} 0.95a+1.15b+21-1.5a-1.5b&=16.7\\ -0.55a-0.35b&=-4.3\end{aligned}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cbegin%7Baligned%7D%200.95a%2B1.15b%2B21-1.5a-1.5b%26%3D16.7%5C%5C%20-0.55a-0.35b%26%3D-4.3%5Cend%7Baligned%7D)
We can solve this using substitution. From the second equation, isolate <em>a: </em>
<em />
<em />
Substitute into the third:
![-0.55(7.6-0.6b)-0.35b=-4.3](https://tex.z-dn.net/?f=-0.55%287.6-0.6b%29-0.35b%3D-4.3)
Distribute and simplify:
![-4.18+0.33b-0.35b=-4.3](https://tex.z-dn.net/?f=-4.18%2B0.33b-0.35b%3D-4.3)
Therefore:
![-0.02b=-0.12\Rightarrow b=6](https://tex.z-dn.net/?f=-0.02b%3D-0.12%5CRightarrow%20b%3D6)
Using the equation for <em>a: </em>
<em />
<em />
<em />
And using the equation for <em>c: </em>
<em />
<em />
<em />
Therefore, Kyle filled 4 10-oz cups, 6 14-oz cups, and 4 20-oz cups.