150 + 20x, where x is the number of cellphones sold
Answer:
![\boxed{\sf k=6}](https://tex.z-dn.net/?f=%5Cboxed%7B%5Csf%20k%3D6%7D)
Step-by-step explanation:
![\sf kx (x-2)+6=0](https://tex.z-dn.net/?f=%5Csf%20kx%20%28x-2%29%2B6%3D0)
Expand brackets.
![\sf kx^2 -2kx+6=0](https://tex.z-dn.net/?f=%5Csf%20kx%5E2%20-2kx%2B6%3D0)
This is in quadratic form.
![\sf ax^2 +bx+c=0](https://tex.z-dn.net/?f=%5Csf%20ax%5E2%20%2Bbx%2Bc%3D0)
Since this is for equal roots:
![\sf b^2 -4ac=0](https://tex.z-dn.net/?f=%5Csf%20b%5E2%20-4ac%3D0)
![\sf a=k\\b=-2k\\c=6](https://tex.z-dn.net/?f=%5Csf%20a%3Dk%5C%5Cb%3D-2k%5C%5Cc%3D6)
![\sf (-2k)^2 -4(k)(6)=0](https://tex.z-dn.net/?f=%5Csf%20%28-2k%29%5E2%20-4%28k%29%286%29%3D0)
![\sf 4k^2-24k=0](https://tex.z-dn.net/?f=%5Csf%204k%5E2-24k%3D0)
![\sf 4k(k-6)=0](https://tex.z-dn.net/?f=%5Csf%204k%28k-6%29%3D0)
![\sf 4k=0\\k=0](https://tex.z-dn.net/?f=%5Csf%204k%3D0%5C%5Ck%3D0)
![\sf k-6=0\\k=6](https://tex.z-dn.net/?f=%5Csf%20k-6%3D0%5C%5Ck%3D6)
Plug k as 0 to check.
![\sf \sf 0x^2 -2(0)x+6=0\\6=0](https://tex.z-dn.net/?f=%5Csf%20%5Csf%200x%5E2%20-2%280%29x%2B6%3D0%5C%5C6%3D0)
False.
So that means k must equal 6.
You surveyed 30 students to see how many CDs they owned.
The number of students who owned 5 - 8 CDs was:
= 15
The number of students who owned 9 - 12 CDs was:
= 10
The number of students who owned 13 - 16 CDs was:
= 5
The number of students who owned 17 - 20 CDs was:
= 0
The total number of students surveyed is the sum of the above:
= 15 + 10 + 5 + 0
= 30 students
30 students were surveyed for this study.
<em>Find out more at brainly.com/question/16372388.</em>