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In a certain company, the formula for maximizing profits is

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In a certain company, the formula for maximizing profits is [#permalink] New post 09 Feb 2009, 02:12
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In a certain company, the formula for maximizing profits is P = -25x^2 + 7500x,, where P is profit and x is the number of machines the company operates in its factory. What value for x will maximize P?

A) 10
B) 50
C) 150
D) 200
E) 300

This one is from IntegratedLearning.

Here's what I did:
[Reveal] Spoiler:
P=-25x2+7500X => P=-50+7500X, to max. P, we need to max X. So I picked E, why isn't that correct?

The OA states: To find a maximum or minimum value of an equation with an exponent in it, you take the derivative of the equation, set it to zero, and solve. I don't really get what that means. So whoever solves it, could you plz post explanation of what the above sentence mean as well?
[Reveal] Spoiler: OA

Last edited by Bunuel on 26 Jan 2014, 03:21, edited 1 time in total.
Edited the question.
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Re: Finding Max or Min value of equation [#permalink] New post 09 Feb 2009, 03:10
wcgmatclub wrote:
This one is from IntegratedLearning. In a certain company, the formula for maximizing profits is P = -25×2 + 7500x, where P is profit and x is the number of machines the company operates in its factory. What value for x will maximize P?

A) 10
B) 50
C) 150
D) 200
E) 300

OC is C

Here's what I did: P=-25x2+7500X => P=-50+7500X, to max. P, we need to max X. So I picked E, why isn't that correct?

The OA states: To find a maximum or minimum value of an equation with an exponent in it, you take the derivative of the equation, set it to zero, and solve. I don't really get what that means. So whoever solves it, could you plz post explanation of what the above sentence mean as well?


Pertaining to your question,
What value for x will maximize P? if you get the derivative of P = -25×2 + 7500x then the equation will bcome,

-50X + 7500 = 0 ( equating to 0 to get max value)
X = 150
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Re: Finding Max or Min value of equation [#permalink] New post 09 Feb 2009, 12:26
Why does P needs to be set to 0 in order to get max value for P. I'm totally lost here.
P = -25×2 + 7500x
If x=150, then P=1124950
If x=300, then P=2249950
2249950>1124950, so P is greater when x=300 vs. x=150.

Why is x=150 the correct answer?
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Re: Finding Max or Min value of equation [#permalink] New post 09 Feb 2009, 13:12
wcgmatclub wrote:
Why does P needs to be set to 0 in order to get max value for P. I'm totally lost here.
P = -25×2 + 7500x
If x=150, then P=1124950
If x=300, then P=2249950
2249950>1124950, so P is greater when x=300 vs. x=150.

Why is x=150 the correct answer?


Not p=0 its dP/dx =firt derviative of P with respect to x
dP/dx =0 = -50x +7500 =0
x=150
Please not that we treated x2= x^2 (please use exponential symbol for that)

P = -25×^2 + 7500x

If x=150, then P=562500
If x=300, then P=0


Do you have knowledge of calculus (Derviatives)..?.
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Re: Finding Max or Min value of equation [#permalink] New post 09 Feb 2009, 15:22
x2suresh wrote:
wcgmatclub wrote:
Why does P needs to be set to 0 in order to get max value for P. I'm totally lost here.
P = -25×2 + 7500x
If x=150, then P=1124950
If x=300, then P=2249950
2249950>1124950, so P is greater when x=300 vs. x=150.

Why is x=150 the correct answer?


Not p=0 its dP/dx =firt derviative of P with respect to x
dP/dx =0 = -50x +7500 =0
x=150
Please not that we treated x2= x^2 (please use exponential symbol for that)

P = -25×^2 + 7500x

If x=150, then P=562500
If x=300, then P=0


Do you have knowledge of calculus (Derviatives)..?.


I took calculus a LONG time ago, so I prob. forgot all of it already. I thought GMAT doesn't test calculus concepts? Why is this "GMAT" type problem requires calculus to solve?
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Re: Finding Max or Min value of equation [#permalink] New post 13 Aug 2010, 22:12
Thanks for this post to have a recall of calculus..."What value for x will maximize P"
Need more clarification on minimum value....

what if require the value of x when profit is lowest???

My understanding is that it comes from the formula for minimize profit. This will be given in question stem... such as this is present here... "the formula for maximizing profits is P = -25x2 + 7500x"....

Please put the correct understanding here.
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Re: Finding Max or Min value of equation [#permalink] New post 14 Aug 2010, 06:32
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appy001 wrote:
Thanks for this post to have a recall of calculus..."What value for x will maximize P"
Need more clarification on minimum value....

what if require the value of x when profit is lowest???

My understanding is that it comes from the formula for minimize profit. This will be given in question stem... such as this is present here... "the formula for maximizing profits is P = -25x2 + 7500x"....

Please put the correct understanding here.

Couple of things:

Quadratic expression ax^2+bx+c reaches its extreme values when x=-\frac{b}{2a}. When a>0 extreme value is minimum value of ax^2+bx+c (maximum value is not limited) and when a<0 extreme value is maximum value of ax^2+bx+c (minimum value is not limited).

You can look at this geometrically: y=ax^2+bx+c when graphed on XY plane gives parabola. When a>0, the parabola opens upward and minimum value of ax^2+bx+c is y-coordinate of vertex, when a<0, the parabola opens downward and maximum value of ax^2+bx+c is y-coordinate of vertex.
Attachment:
Math_cg_20 (1).png
Math_cg_20 (1).png [ 18.71 KiB | Viewed 13469 times ]


Examples:
Expression 5x^2-10x+20 reaches its minimum when x=-\frac{b}{2a}=-\frac{-10}{2*5}=1, so minimum value is 5x^2-10x+20=5*1^2-10*1+20=15.

Expression -5x^2-10x+20 reaches its maximum when x=-\frac{b}{2a}=-\frac{-10}{2*(-5)}=-1, so maximum value is -5x^2-10x+20=-5*(-1)^2-10*(-1)+20=25.

Back to the original question:

In a certain company, the formula for maximizing profits is P = -25x^2 + 7500x, where P is profit and x is the number of machines the company operates in its factory. What value for x will maximize P?

A) 10
B) 50
C) 150
D) 200
E) 300

P=-25x^2+7500x reaches its maximum (as a=-25<0) when x=-\frac{b}{2a}=-\frac{7500}{2*(-25)}=150.

Answer: C.

As for the minimum value of P: minimum value of P is not limited (x increase to +infinity --> P decreases to -infinity).

Hope it helps.
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Re: Finding Max or Min value of equation [#permalink] New post 15 Aug 2010, 17:11
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If you understand Calculus, this is the easy way of solving it. Nobody else mentioned, but you also need to take the second derivative.

f(x) = -25x^2 + 7500x

f'(x) = -50x + 7500

-50x + 7500 = 0
7500 = 50x
x = 150

f''(x) = -50

If the second derivative is negative, it is a maximum. If it is positive, it is a minimum.
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Re: Finding Max or Min value of equation [#permalink] New post 15 Aug 2010, 19:17
Hey Bro,
Thanks a lot..."If the second derivative is negative, it is a maximum. If it is positive, it is a minimum. "...

I was looking for this only....its really long long time I left calculus so was trying some lead...Kudos Given..
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Re: In a certain company, the formula for maximizing profits is [#permalink] New post 11 Sep 2013, 08:36
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Re: In a certain company, the formula for maximizing profits is [#permalink] New post 11 Sep 2013, 12:18
Hello

I had two points to share
1) Please confirm that I understand the equation in the question correctly : P=(-25)(2)+ (7500x). If I'm reading it correctly, then how does this equation turn into -50x+7500x?

2) How testable is this content on actual GMAT test? because I looked into the official guide testable topics as well as Manhattan books and it seems that calculus is not one of the topics. Where can I find this content to study?
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Re: In a certain company, the formula for maximizing profits is [#permalink] New post 25 Jan 2014, 23:52
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wcgc wrote:
In a certain company, the formula for maximizing profits is P = -25×2 + 7500x, where P is profit and x is the number of machines the company operates in its factory. What value for x will maximize P?

A) 10
B) 50
C) 150
D) 200
E) 300

This one is from IntegratedLearning.

Here's what I did:
[Reveal] Spoiler:
P=-25x2+7500X => P=-50+7500X, to max. P, we need to max X. So I picked E, why isn't that correct?

The OA states: To find a maximum or minimum value of an equation with an exponent in it, you take the derivative of the equation, set it to zero, and solve. I don't really get what that means. So whoever solves it, could you plz post explanation of what the above sentence mean as well?


People, please write the equation properly.

I was wondering how p = -50 + 7500x we can solve this question for 5 mins :x :twisted: :evil:
It is simply as increasing functions.

Please edit the question and write P = -25 * x^2 + 7500x

We can solve the above problem by calculas Maxima and minima or by using the perfect score approach.
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Re: In a certain company, the formula for maximizing profits is [#permalink] New post 26 Jan 2014, 03:22
Expert's post
kinjiGC wrote:
wcgc wrote:
In a certain company, the formula for maximizing profits is P = -25×2 + 7500x, where P is profit and x is the number of machines the company operates in its factory. What value for x will maximize P?

A) 10
B) 50
C) 150
D) 200
E) 300

This one is from IntegratedLearning.

Here's what I did:
[Reveal] Spoiler:
P=-25x2+7500X => P=-50+7500X, to max. P, we need to max X. So I picked E, why isn't that correct?

The OA states: To find a maximum or minimum value of an equation with an exponent in it, you take the derivative of the equation, set it to zero, and solve. I don't really get what that means. So whoever solves it, could you plz post explanation of what the above sentence mean as well?


People, please write the equation properly.

I was wondering how p = -50 + 7500x we can solve this question for 5 mins :x :twisted: :evil:
It is simply as increasing functions.

Please edit the question and write P = -25 * x^2 + 7500x

We can solve the above problem by calculas Maxima and minima or by using the perfect score approach.

______
Done. Thank you.
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COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: In a certain company, the formula for maximizing profits is [#permalink] New post 09 Feb 2014, 18:08
If you're not comfortable with calculus, here is how I would do it.

Recognize that 25 is a factor of 7500. If we take this out, we have two parts to the equation:

-X^2 & 300X

One part of the equation brings our value down, whereas the other part brings our value up. At this point, we can test the numbers in the answer choice. Notice that they are very straight forward to square, and multiplication by 300 is very easy.



A) 10 - 3000 - 100 = 2900
B) 50 - 15000 - 2500 = 12500
C) 150 - 45000 - 22500 = 22500
D) 200 - 60000 - 40000 = 20000
E) 300 - recognize that this is zero

Therefore, answer is 150.

If you are able to spot the 25 in 7500, you can go through this process in and around 2 minutes. Also, if you tested C or D first, you'd recognize that A and B would never be able to reach their output, and spotting that E makes the equation equal to 0, there is only 2 numbers you would need to test.

Hope this helps those - like myself - who haven't thought about calculus for over half a decade.
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Re: In a certain company, the formula for maximizing profits is [#permalink] New post 15 Feb 2014, 22:02
My approach is just plugging ,
X = 150 , where p = 562500
X = 300 , p = 0 , x = 200 = 500000
so C
Re: In a certain company, the formula for maximizing profits is   [#permalink] 15 Feb 2014, 22:02
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