SOLUTION: 18) The We Make Widgets Company manufactures widgets. They find that when they charge d dollars for each widget, their income, I(d) can be expressed by the formular I(d) = -120d^2

Algebra ->  Trigonometry-basics -> SOLUTION: 18) The We Make Widgets Company manufactures widgets. They find that when they charge d dollars for each widget, their income, I(d) can be expressed by the formular I(d) = -120d^2       Log On


   



Question 173539This question is from textbook Amsco's Preparing for the Regents Examination Mathematics B
: 18) The We Make Widgets Company manufactures widgets. They find that when they charge d dollars for each widget, their income, I(d) can be expressed by the formular I(d) = -120d^2 + 14,400d + 100. What price should they charge to maximize their income? If this price is charged, what is their maxium income?
Please can someone help me and show work, step by step?
Thank you so much for your time.
Happy Holidays
This question is from textbook Amsco's Preparing for the Regents Examination Mathematics B

Found 2 solutions by nerdybill, josmiceli:
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
18) The We Make Widgets Company manufactures widgets. They find that when they charge d dollars for each widget, their income, I(d) can be expressed by the formular I(d) = -120d^2 + 14,400d + 100. What price should they charge to maximize their income? If this price is chargeThe d coordinate = -14400/2(-120)
d, what is their maxium income?
.
Looking at the 'a' coefficient of the given equation:
I(d) = -120d^2 + 14400d + 100
.
We see that it is negative -- meaning that it is a parabola that is opened downward. So, if we simply find the "vertex" of the equation, we'll find the "maximum".
.
For additional info on vertex form of a parabola:
http://www.mathwarehouse.com/geometry/parabola/standard-and-vertex-form.php
.
The vertex is located at:
The d coordinate = -b/2a
The d coordinate = -14400/2(-120)
The d coordinate = -14400/(-240)
The d coordinate = 60
What price should they charge to maximize their income? $60
.
what is their maxium income?
Plug it back into the original formula:
.
I(d) = -120d^2 + 14,400d + 100
I(60) = -120(60)^2 + 14,400(60) + 100
I(60) = -120(3600) + 14400(60) + 100
I(60) = -432000 + 864000 + 100
I(60) = 432000 + 100
I(60) = $432,100

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
I always think of the maximum as being exactly between
the 2 roots of a parabola (where it crosses the x-axis
The quadratic formula finds the roots
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
There is a (+) and a (-) answer, and thoses are the roots
If you rewrite the formula like this:
x+=+-b%2F2a+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%2F%282%2Aa%29+
you can see that -b%2F2a is in the middle and you add
the 2nd term to get the larger root and subtract the 2nd
term to get the smaller root.
So, you just have to find -b%2F2a to find the maximum
The general formula for finding roots is
ax%5E2+%2B+bx+%2B+c+=+0
The equation in the problem is (d replaces x)
I%28d%29+=+-120d%5E2+%2B+14400d+%2B+100
a+=+-120
b+=+14400
c+=+100
-b%2F2a+=+-14400%2F%28-240%29
-b%2F2a+=+60
This says d+=+60 when I%28d%29 is a maximum
$60 /widget should be charged to maximize income
----------------
The problem wants to know what that income is
I%28d%29+=+-120d%5E2+%2B+14400d+%2B+100
I%2860%29+=+-120%2A60%5E2+%2B+14400%2A60+%2B+100
I%2860%29+=+-120%2A3600+%2B+864000+%2B+100
I%2860%29+=+-432000+%2B+864000+%2B+100
I%2860%29+=+432100
The maximum income is $432,100
You can check the answers by making d a little
bit less, say 59.9 and finding I%28d%29
and a little bit more, say 60.1 and finding
I%28d%29 In both cases, I%28d%29 should be
less than 432100