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# when a CD player is proiced at \$300 per unit, a store sells

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Manager
Joined: 25 Jun 2003
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when a CD player is proiced at \$300 per unit, a store sells [#permalink]

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14 Jul 2003, 07:49
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when a CD player is proiced at \$300 per unit, a store sells 15 units per week . Each time the price is reduced by \$10, however, the sales increase 2units per week. What selling price will result in weekly revenues of \$7000 ?

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Brainless

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Manager
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14 Jul 2003, 09:18
Selling price will be 200.

As 35 units shall be sold then.

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Intern
Joined: 31 May 2003
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try to solve this equation [#permalink]

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14 Jul 2003, 10:35
(300-a)(15+ 2 (a/10)) = 7000

you will get a=100 or 125,

since 125 gives you unbelievably decimaled answer, you know you should choose 100. Then use 300-100=200

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SVP
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14 Jul 2003, 10:40
(300-10x)(15+2x)=7000
2x^2-45x+250=7000
x=10

Price = 300-10*10=200

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Director
Joined: 03 Jul 2003
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14 Jul 2003, 14:35
stolyar wrote:
(300-10x)(15+2x)=7000
2x^2-45x+250=7000
x=10

Price = 300-10*10=200

How do you get the equation in 2nd line?
I broke my head for ten minutes to slove this equation!
Is there is nifty way to solve these kind of Quad equations?

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Manager
Joined: 08 Apr 2003
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15 Jul 2003, 03:02
stolyar wrote:
(300-10x)(15+2x)=7000
2x^2-45x+250=7000
x=10

Price = 300-10*10=200

How do you get the equation in 2nd line?
I broke my head for ten minutes to slove this equation!
Is there is nifty way to solve these kind of Quad equations?

I used thr trial and error method. It landed out to be fastest. As fasr as i know GMAT doesnt involve complex calculations. They are not checking your skills to solve complex quadratic. The want quick and efficient methods to be arrive at the answer.

HTH:)

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Manager
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15 Jul 2003, 04:54
As some of the math wizards already pointed out , there is no much brain to be used on this question. The answer choices contained were 175 and 200 along with other values. Most of us (including me ) chose 175 ( in 20 secs ) which is clearly wrong !! CD price is decreasing by 10s . If you ask any 1st grader to count by 10, he / she wont find 175..

Well known GMAT trap !!
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Brainless

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15 Jul 2003, 04:54
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