SOLUTION: When a vendor prices key chains at $5 each, she sells 210 key chains. For each $1 she raises the price, she sells 10 fewer key chains. USE AN EQUATION to determine what she should

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Question 813641: When a vendor prices key chains at $5 each, she sells 210 key chains. For each $1 she raises the price, she sells 10 fewer key chains. USE AN EQUATION to determine what she should charge to maximize her revenue from sales.
Answer by TimothyLamb(4379) About Me  (Show Source):
You can put this solution on YOUR website!
use the revenue equation:
r = p * n
where
p = price per item
n = number of items sold
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because we know that changing the price (p) also changes the number sold (n), we need to introduce a variable to the revenue equation to measure the changes in p and n.
---
so just make up a variable, call it x, such that:
p + x means a one dollar price increase and
p - x means a one dollar price decrease and
n + x means a one item number-sold increase and
n - x means a one item number-sold decrease
---
for each $1 price increase (p + x) there are 10 fewer items sold (n - 10x), so:
---
r = (p + x) * (n - 10x)
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we know that at $5 per item, she sells 210 items, so:
r = (5 + x) * (210 - 10x)
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r = (5 + x) * (210 - 10x)
r = 1050 - 50x + 210x - 10xx
r = -10xx + 160x + 1050
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the above quadratic equation is in standard form, with a=-10, b=160, and c=1050
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to solve the quadratic equation, plug this:
-10 160 1050
into this: https://sooeet.com/math/quadratic-equation-solver.php
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Answer 1:
the quadratic equation has a maximum at: ( x=8, r=1690 ), so:
maximum revenue is $1690
when price per item is $8
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