Answer:
1. <u>Cost per customer</u>: 10 + x
<u>Average number of customers</u>: 16 - 2x
![\textsf{2.} \quad -2x^2-4x+160\geq 130](https://tex.z-dn.net/?f=%5Ctextsf%7B2.%7D%20%5Cquad%20%20-2x%5E2-4x%2B160%5Cgeq%20130)
3. $10, $11, $12 and $13
Step-by-step explanation:
<u>Given information</u>:
- $10 = cost of buffet per customer
- 16 customers choose the buffet per hour
- Every $1 increase in the cost of the buffet = loss of 2 customers per hour
- $130 = minimum revenue needed per hour
Let x = the number of $1 increases in the cost of the buffet
<u>Part 1</u>
<u></u>
<u>Cost per customer</u>: 10 + x
<u>Average number of customers</u>: 16 - 2x
<u>Part 2</u>
The cost per customer multiplied by the number of customers needs to be <u>at least</u> $130. Therefore, we can use the expressions found in part 1 to write the <u>inequality</u>:
![(10 + x)(16 - 2x)\geq 130](https://tex.z-dn.net/?f=%2810%20%2B%20x%29%2816%20-%202x%29%5Cgeq%20%20130)
![\implies 160-20x+16x-2x^2\geq 130](https://tex.z-dn.net/?f=%5Cimplies%20160-20x%2B16x-2x%5E2%5Cgeq%20130)
![\implies -2x^2-4x+160\geq 130](https://tex.z-dn.net/?f=%5Cimplies%20-2x%5E2-4x%2B160%5Cgeq%20130)
<u>Part 3</u>
To determine the possible buffet prices that Noah could charge and still maintain the restaurant owner's revenue requirements, solve the inequality:
![\implies -2x^2-4x+160\geq 130](https://tex.z-dn.net/?f=%5Cimplies%20-2x%5E2-4x%2B160%5Cgeq%20130)
![\implies -2x^2-4x+30\geq 0](https://tex.z-dn.net/?f=%5Cimplies%20-2x%5E2-4x%2B30%5Cgeq%200)
![\implies -2(x^2+2x-15)\geq 0](https://tex.z-dn.net/?f=%5Cimplies%20-2%28x%5E2%2B2x-15%29%5Cgeq%200)
![\implies x^2+2x-15\leq 0](https://tex.z-dn.net/?f=%5Cimplies%20x%5E2%2B2x-15%5Cleq%20%200)
![\implies (x-3)(x+5)\leq 0](https://tex.z-dn.net/?f=%5Cimplies%20%28x-3%29%28x%2B5%29%5Cleq%20%200)
Find the roots by equating to zero:
![\implies (x-3)(x+5)=0](https://tex.z-dn.net/?f=%5Cimplies%20%28x-3%29%28x%2B5%29%3D0)
![x-3=0 \implies x=3](https://tex.z-dn.net/?f=x-3%3D0%20%5Cimplies%20x%3D3)
![x+5=0 \implies x=-5](https://tex.z-dn.net/?f=x%2B5%3D0%20%5Cimplies%20x%3D-5)
Therefore, the roots are x = 3 and x = -5.
<u>Test the roots</u> by choosing a value between the roots and substituting it into the original inequality:
![\textsf{At }x=2: \quad -2(2)^2-4(2)+160=144](https://tex.z-dn.net/?f=%5Ctextsf%7BAt%20%7Dx%3D2%3A%20%5Cquad%20-2%282%29%5E2-4%282%29%2B160%3D144)
As 144 ≥ 130, the <u>solution</u> to the inequality is <u>between the roots</u>:
-5 ≤ x ≤ 3
To find the range of possible buffet prices Noah could charge and still maintain a minimum revenue of $130, substitute x = 0 and x = 3 into the expression for "cost per customer.
[Please note that we cannot use the negative values of the possible values of x since the question only tells us information about the change in average customers per hour considering an <em>increase </em>in cost. It does not confirm that if the cost is reduced (less than $10) the number of customers <em>increases </em>per hour.]
<u>Cost per customer</u>:
![x =0 \implies 10 + 0=\$10](https://tex.z-dn.net/?f=x%20%3D0%20%5Cimplies%2010%20%2B%200%3D%5C%2410)
![x=3 \implies 10+3=\$13](https://tex.z-dn.net/?f=x%3D3%20%5Cimplies%2010%2B3%3D%5C%2413)
Therefore, the possible buffet prices Noah could charge are:
$10, $11, $12 and $13.