GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 19 Nov 2018, 01:51

INSEAD R1 Results This Week!

First Decision Reported on Decision Tracker  |  Join INSEAD Chat to Calm Your Nerves & Catch the Latest Action


Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in November
PrevNext
SuMoTuWeThFrSa
28293031123
45678910
11121314151617
18192021222324
2526272829301
Open Detailed Calendar
  • How to QUICKLY Solve GMAT Questions - GMAT Club Chat

     November 20, 2018

     November 20, 2018

     09:00 AM PST

     10:00 AM PST

    The reward for signing up with the registration form and attending the chat is: 6 free examPAL quizzes to practice your new skills after the chat.
  • The winning strategy for 700+ on the GMAT

     November 20, 2018

     November 20, 2018

     06:00 PM EST

     07:00 PM EST

    What people who reach the high 700's do differently? We're going to share insights, tips and strategies from data we collected on over 50,000 students who used examPAL.

A store sells a certain product at a fixed price per unit. A

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Manager
Manager
avatar
Joined: 22 Dec 2011
Posts: 238
A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post Updated on: 04 Oct 2012, 11:27
4
13
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

70% (03:04) correct 30% (03:16) wrong based on 416 sessions

HideShow timer Statistics

A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?

A. 10
B. 15
C. 20
D. 25
E. 30

Is there any easy way to solve this problem? Ans is the real exam going to have these sort of problems?

Cheers

Originally posted by Jp27 on 04 Oct 2012, 10:35.
Last edited by Bunuel on 04 Oct 2012, 11:27, edited 1 time in total.
RENAMED THE TOPIC.
Most Helpful Expert Reply
Magoosh GMAT Instructor
User avatar
G
Joined: 28 Dec 2011
Posts: 4488
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 04 Oct 2012, 13:52
10
5
Jp27 wrote:
A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?
A. 10
B. 15
C. 20
D. 25
E. 30

Is there any easy way to solve this problem? And is the real exam going to have these sort of problems?

Dear Jp27,

I'm happy to help with this. :-) This problem is very hard --- definitely an upper 700 level question. If you are doing very well on the Quant section, the CAT could feed you a question like this.

This question is a very challenging if you take an algebraic approach, but it's remarkably simple if you backsolve.

Let's start with (C).
Assume q = 20 units
If we can buy 20 units, they must cost a price of 300/20 = $15
Lower the price $5 to a new price of $10 --- then we could buy 300/10 = 30 units (10 more than the original case)
Raise the price $5 to a new price of $20 ---- then we could buy 300/20 = 15 units (5 fewer than the original case)

This is the case for which we are looking ----- the increase in units from a $5 decrease in price is twice as much as the decrease in units from a $5 increase in price.

Does this make sense?

Mike :-)
_________________

Mike McGarry
Magoosh Test Prep


Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)

Most Helpful Community Reply
Intern
Intern
avatar
Joined: 04 Dec 2012
Posts: 13
GMAT 1: 680 Q44 V38
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 03 Mar 2013, 05:39
15
6
Hello !

I was reviewing some questions and I think this one is not as difficult as it seems. I solved it in less than 2 minutes using equations solving so I felt like it could be useful to other people :

We can write the following equations :

(1) pq = 300
(2) (q+2n)(p-5) = 300
(3) (q-n)(p+5) = 300

Distribute (2) and (3) :

(2) qp -5q +2np -10n = 300
(3) qp +5q -np - 5n = 300

Add them together :

(2) + (3) : 2qp +np -15n = 600
Thanks to (1) you get : np-15n = 0 or n(p-15) = 0

Since n can't be 0 ( it would mean that a lower or higher price doesn't affect the total price and quantities ) you have p-15 = 0 and p =15. With (1), you get q = 300/15 = 20

I know it seems time consuming but it worked for me. And I usually don't like picking numbers..
General Discussion
Senior Manager
Senior Manager
User avatar
Joined: 28 Jun 2009
Posts: 387
Location: United States (MA)
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 04 Oct 2012, 14:09
2
It got too complicated when I used algebra. Using plugging in, it was quite fast.

Price Quantity total value
p q pq = 300
p-5 q+2n (p-5)(q+2n) = 300
p+5 q-n (p+5)(q-n) = 300

Solving three equations for three unknowns. Tough!!

Plugging in, I always start with C. C was the answer here, so saved calculation!

Putting values in above equations:

Price Quantity total value
15 20 300
10 20+2n 300 -> 10(20 + 2n)=300 -> 200 +20n = 300 -> 20n = 100 -> n =5
20 15 300

So q = 20 satisfies all equations!!

What is the source?
Manager
Manager
avatar
B
Joined: 26 Jul 2011
Posts: 93
Location: India
WE: Marketing (Manufacturing)
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 04 Oct 2012, 23:02
1
As it is said for GMAT "whenever you see yourself dealing with some extra long equations or calculations trust!! there is an easy way out" here in this case back solving makes this question way too easy.

B is the answer
Manager
Manager
avatar
Joined: 22 Dec 2011
Posts: 238
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 06 Oct 2012, 20:52
mikemcgarry wrote:
Jp27 wrote:
A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?
A. 10
B. 15
C. 20
D. 25
E. 30

Is there any easy way to solve this problem? And is the real exam going to have these sort of problems?

Dear Jp27,

I'm happy to help with this. :-) This problem is very hard --- definitely an upper 700 level question. If you are doing very well on the Quant section, the CAT could feed you a question like this.

This question is a very challenging if you take an algebraic approach, but it's remarkably simple if you backsolve.

Let's start with (C).
Assume q = 20 units
If we can buy 20 units, they must cost a price of 300/20 = $15
Lower the price $5 to a new price of $10 --- then we could buy 300/10 = 30 units (10 more than the original case)
Raise the price $5 to a new price of $20 ---- then we could buy 300/20 = 15 units (5 fewer than the original case)

This is the case for which we are looking ----- the increase in units from a $5 decrease in price is twice as much as the decrease in units from a $5 increase in price.

Does this make sense?

Mike :-)


Thanks Mike. It does, especially the way you have circumvented calculating the variable N. I guess all the thinking goes before even touching the pen!

cheers
Intern
Intern
avatar
Status: Fighting to kill GMAT
Joined: 23 Sep 2012
Posts: 28
Location: United States
Concentration: International Business, General Management
Schools: Duke '16
GPA: 3.8
WE: General Management (Other)
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 07 Oct 2012, 07:57
piyatiwari wrote:
It got too complicated when I used algebra. Using plugging in, it was quite fast.

Price Quantity total value
p q pq = 300
p-5 q+2n (p-5)(q+2n) = 300
p+5 q-n (p+5)(q-n) = 300

Solving three equations for three unknowns. Tough!!

Plugging in, I always start with C. C was the answer here, so saved calculation!

Putting values in above equations:

Price Quantity total value
15 20 300
10 20+2n 300 -> 10(20 + 2n)=300 -> 200 +20n = 300 -> 20n = 100 -> n =5
20 15 300

So q = 20 satisfies all equations!!

What is the source?


Is there any reason why you start with C while using POE? What if the numbers are not given in a particular order (ascending here)? Do you use the same strategy in other question types?
_________________

Kudos is the currency of appreciation.



You can have anything you want if you want it badly enough. You can be anything you want to be and do anything you set out to accomplish, if you hold to that desire with the singleness of purpose. ~William Adams

Many of life's failures are people who did not realize how close to success they were when they gave up. ~Thomas A. Edison

Wir müssen wissen, Wir werden wissen. (We must know, we will know.) ~Hilbert

Senior Manager
Senior Manager
User avatar
Joined: 28 Jun 2009
Posts: 387
Location: United States (MA)
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 07 Oct 2012, 08:53
closed271 wrote:
Is there any reason why you start with C while using POE? What if the numbers are not given in a particular order (ascending here)? Do you use the same strategy in other question types?


No reason. I always start with option C while using plugging in.

MGMAT advanced math book has some nice techniques about ruling out option choices.
But here, I didn't use any of those.
Director
Director
User avatar
Joined: 22 Mar 2011
Posts: 601
WE: Science (Education)
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 08 Oct 2012, 08:46
1
navigator123 wrote:
Jp27 wrote:
A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?

A. 10
B. 15
C. 20
D. 25
E. 30

Is there any easy way to solve this problem? Ans is the real exam going to have these sort of problems?

Cheers


Since from the options is of pure chance, one would end up losing lots of time.

Any other solution for this question?


Back to the basics.
Write down the prices and corresponding quantities using the given answers. You will get a small table:

(Q, P)
(10, 30)
(15, 20)
(20, 15)
(25, 12)
(30, 10)

From the given information, about raising/reducing the price, you can conclude the following about the prices and corresponding quantities:

Q+2N P-5
Q P
Q-N P+5

The corresponding prices for the quantities Q+2N, Q, and Q-N are three consecutive multiples of 5: P-5, P, and P+5. From the table, the prices should be 10, 15, and 20, and thus the quantity should be 20.

Answer C.

Remark: this is my corrected post, as in my previous one, I mixed up prices and quantities. If somebody saw it, please, just forget about it.
_________________

PhD in Applied Mathematics
Love GMAT Quant questions and running.

Magoosh GMAT Instructor
User avatar
G
Joined: 28 Dec 2011
Posts: 4488
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 08 Oct 2012, 12:00
5
closed271 wrote:
Is there any reason why you start with C while using POE? What if the numbers are not given in a particular order (ascending here)? Do you use the same strategy in other question types?

On official GMAT problems, if the answer choices are all single numbers, those numbers will be in numerical order. This is true on all official material and all high quality material, and therefore it's an excellent test of how authentic a given prep source is --- if you see a number of questions with the answers out of order, that's a red flag --- you should question whether that source is trustworthy. Some GMAT prep sources are excellent, and some are not worth the paper on which they are printed.

The reason we start with the middle answer (i.e. (C) on official material) is so that we know which way to go if our first choice is not right. Consider this hypothetical question:
Frank started with X money. He bought blah blah, blah blah, blah % of blah, etc etc and was left with $41.50 in cash after those purchases. What was Frank's original starting amount?
(A) $100
(B) $120
(C) $150
(D) $180
(E) $200


I will start with (C) 150 ----- if by chance I'm right, that's great. If I wind up with more leftover cash than $41.50, I know I started with too much --- I can eliminate (C) & (D) & (E). If I wind up with less leftover cash than $41.50, I know I started with too little --- I can eliminate (A) & (B) & (C). Does that make sense?

Mike :-)
_________________

Mike McGarry
Magoosh Test Prep


Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)

Manager
Manager
avatar
Joined: 26 Jul 2012
Posts: 60
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 10 Nov 2012, 14:00
Even with plugging in this is a humdinger problem!

I tried the algebraic approach first and got stuck. Finally, took a guess.

With plugging in, I will try to time myself but it will take exactly two minutes still.

Start with C (so we know which direction to go in)

Case 1:
(x) = Price of the unit
(q) = # of units
Let q = 20
Therefore, x = 15 because qx = 300
Case 2:
x-5 = 10
Given: q + 2n = 30; therefore:
20 + 2n = 30
2n = 10
n = 5

Case 3:
x+5 = 20
Given : q - n = 15
20 - 5 = 15
Done. D is the answer because the equation checks out!
Manager
Manager
User avatar
Status: struggling with GMAT
Joined: 06 Dec 2012
Posts: 135
Location: Bangladesh
Concentration: Accounting
GMAT Date: 04-06-2013
GPA: 3.65
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 28 Mar 2013, 03:56
pancakeFR wrote:
Hello !

I was reviewing some questions and I think this one is not as difficult as it seems. I solved it in less than 2 minutes using equations solving so I felt like it could be useful to other people :

We can write the following equations :

(1) pq = 300
(2) (q+2n)(p-5) = 300
(3) (q-n)(p+5) = 300

Distribute (2) and (3) :

(2) qp -5q +2np -10n = 300
(3) qp +5q -np - 5n = 300

Add them together :

(2) + (3) : 2qp +np -15n = 600
Thanks to (1) you get : np-15n = 0 or n(p-15) = 0

Since n can't be 0 ( it would mean that a lower or higher price doesn't affect the total price and quantities ) you have p-15 = 0 and p =15. With (1), you get q = 300/15 = 20

I know it seems time consuming but it worked for me. And I usually don't like picking numbers..


Hi
this also works for me.Most of the times i can`t pick the number.1 kudos for u
Intern
Intern
avatar
Joined: 22 Jan 2010
Posts: 24
Location: India
Concentration: Finance, Technology
GPA: 3.5
WE: Programming (Telecommunications)
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 28 Mar 2013, 04:08
7
3
Let p be price per unit.

From the first condition we get pq = 300.

From the other conditions we get,
(p-5)(q+2n) = pq
=> pq -5q + 2pn - 10n = pq
=> 5q = 2pn - 10n

(p+5)(q-n) = pq
=> pq + 5q - pn -5n = pq
=> 5q = pn + 5n -------(3)

so, 2pn - 10n = pn + 5n
=> pn = 15n
=> p = 15
Then q = 300/15 = 20.

Answer : Option C.
-------------------------------------
Please press KUDOS if you like my post.
Manager
Manager
avatar
Joined: 26 Sep 2013
Posts: 196
Concentration: Finance, Economics
GMAT 1: 670 Q39 V41
GMAT 2: 730 Q49 V41
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 22 Oct 2013, 10:48
mikemcgarry wrote:
Jp27 wrote:
A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?
A. 10
B. 15
C. 20
D. 25
E. 30

Is there any easy way to solve this problem? And is the real exam going to have these sort of problems?

Dear Jp27,

I'm happy to help with this. :-) This problem is very hard --- definitely an upper 700 level question. If you are doing very well on the Quant section, the CAT could feed you a question like this.

This question is a very challenging if you take an algebraic approach, but it's remarkably simple if you backsolve.

Let's start with (C).
Assume q = 20 units
If we can buy 20 units, they must cost a price of 300/20 = $15
Lower the price $5 to a new price of $10 --- then we could buy 300/10 = 30 units (10 more than the original case)
Raise the price $5 to a new price of $20 ---- then we could buy 300/20 = 15 units (5 fewer than the original case)

This is the case for which we are looking ----- the increase in units from a $5 decrease in price is twice as much as the decrease in units from a $5 increase in price.

Does this make sense?

Mike :-)



I don't get this at all;

based on the first part: 300/(20+2n)=10 (since q=20, the original price was 15 per unit, minus 5 gives you 10), then the 2nd piece gives you 300/(20-n)=20...and I get stuck. What do I do with those two facts. Also, the part highlighted in red, how do you you know you're looking for that case?
Magoosh GMAT Instructor
User avatar
G
Joined: 28 Dec 2011
Posts: 4488
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 22 Oct 2013, 11:02
2
AccipiterQ wrote:
A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?
A. 10
B. 15
C. 20
D. 25
E. 30

This is the case for which we are looking ----- the increase in units from a $5 decrease in price is twice as much as the decrease in units from a $5 increase in price.

I don't get this at all;

based on the first part: 300/(20+2n)=10 (since q=20, the original price was 15 per unit, minus 5 gives you 10), then the 2nd piece gives you 300/(20-n)=20...and I get stuck. What do I do with those two facts. Also, the part highlighted in red, how do you you know you're looking for that case?

Dear AccipiterQ,
You seem to be doing the problem with a mix of algebra and backsolving together, which is very very confusing. Do one or the other.

For this problem, I believe backsolving is much easier.
As always, start with (C) --- suppose q = 20.
That means original price is $300/20 = $15.
Now, don't do algebra here --- just follow the numerical consequences.
If the price is lowered $5 to $10, then we could buy $300/$10 = 30 items, which is q + 10
If the price is raised $5 to $20, then we could buy $300/$20 = 15 items, which is q - 5
The difference between (q + 2p) and (q - p) is that the distance between q and the higher item number (at the lower price) is TWICE the distance between q and the lower item number (at the higher price). Well, here, 10 is twice 5, so we know we have met that condition.

Does all this make sense?
Mike :-)
_________________

Mike McGarry
Magoosh Test Prep


Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)

Manager
Manager
avatar
Joined: 26 Sep 2013
Posts: 196
Concentration: Finance, Economics
GMAT 1: 670 Q39 V41
GMAT 2: 730 Q49 V41
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 22 Oct 2013, 12:51
mikemcgarry wrote:
AccipiterQ wrote:
A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?
A. 10
B. 15
C. 20
D. 25
E. 30

This is the case for which we are looking ----- the increase in units from a $5 decrease in price is twice as much as the decrease in units from a $5 increase in price.

I don't get this at all;

based on the first part: 300/(20+2n)=10 (since q=20, the original price was 15 per unit, minus 5 gives you 10), then the 2nd piece gives you 300/(20-n)=20...and I get stuck. What do I do with those two facts. Also, the part highlighted in red, how do you you know you're looking for that case?

Dear AccipiterQ,
You seem to be doing the problem with a mix of algebra and backsolving together, which is very very confusing. Do one or the other.

For this problem, I believe backsolving is much easier.
As always, start with (C) --- suppose q = 20.
That means original price is $300/20 = $15.
Now, don't do algebra here --- just follow the numerical consequences.
If the price is lowered $5 to $10, then we could buy $300/$10 = 30 items, which is q + 10
If the price is raised $5 to $20, then we could buy $300/$20 = 15 items, which is q - 5
The difference between (q + 2p) and (q - p) is that the distance between q and the higher item number (at the lower price) is TWICE the distance between q and the lower item number (at the higher price). Well, here, 10 is twice 5, so we know we have met that condition.

Does all this make sense?
Mike :-)



aaaah I get it now, I was creating a stew of algebra & backsolving. Makes perfect sense, thanks!
Intern
Intern
avatar
Joined: 02 Oct 2014
Posts: 1
A store sells a certain product at a fixed price per unit.  [#permalink]

Show Tags

New post 29 Dec 2014, 15:16
A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?

a: 10 b: 15 c: 20 d: 25 e: 30

in the solution, they say, this problem is to hard to solve with algebra, so they just put in the answer choices and figure out what ist right... That is ok for me, but I don't get how you can se if a problem of this kind is solvable quickly or if it is better just to go with the answer options. Has anybody an advice about that? The problem above didn't look that hard for me so I spent 2 min with it and got the wrong answer:)
Director
Director
User avatar
G
Status: Tutor - BrushMyQuant
Joined: 05 Apr 2011
Posts: 610
Location: India
Concentration: Finance, Marketing
Schools: XLRI (A)
GMAT 1: 700 Q51 V31
GPA: 3
WE: Information Technology (Computer Software)
Re: A store sells a certain product at a fixed price per unit.  [#permalink]

Show Tags

New post 29 Dec 2014, 19:06
1
Am not a big fan of substitution so am posting a solution using algebra (doesn't look like a tough equation to solve)
We just need to eliminate the variables which we don't really need to compute

If we notice the three equations then we can get that "n" is the variable which is making the equations complex for us. So, let eliminate n first
Let price be p
pq = 300
(p-5)*(q+2n) = 300 => q+2n = 300/(p-5) ...(1)
(p+5)*(q-n) = 300 => q-n = 300/(p+5) => 2q - 2n = 600/(p+5) ..(2)
Adding (1) and (2), we get
3q = 300/(p-5) + 600/(p-5)

Now, we just have two equations in p and q. (Solving for p as the equation looks easy to me)
put q = 300/p
900/p = 300/(p-5) + 600/(p+5)
3/p = (p+5 +2p - 10)/(p^2-25)
simplifying we get
3p^2 - 75 - 3p^2 + 5p =0
p =15
=> q = 20


edsafari wrote:
A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?

a: 10 b: 15 c: 20 d: 25 e: 30

in the solution, they say, this problem is to hard to solve with algebra, so they just put in the answer choices and figure out what ist right... That is ok for me, but I don't get how you can se if a problem of this kind is solvable quickly or if it is better just to go with the answer options. Has anybody an advice about that? The problem above didn't look that hard for me so I spent 2 min with it and got the wrong answer:)

_________________

Ankit

Check my Tutoring Site -> Brush My Quant

GMAT Quant Tutor
How to start GMAT preparations?
How to Improve Quant Score?
Gmatclub Topic Tags
Check out my GMAT debrief

How to Solve :
Statistics || Reflection of a line || Remainder Problems || Inequalities

Director
Director
User avatar
G
Joined: 23 Jan 2013
Posts: 569
Schools: Cambridge'16
Re: A store sells a certain product at a fixed price per unit.  [#permalink]

Show Tags

New post 29 Dec 2014, 23:47
1
have three equations

300/q=p

300/q+2n=p-5

300/q-n=p+5

one option is solving algebraically but it is too long for three variables

started backsolve from q=20 (C)

find that p=15, n=5 and all is OK in this case

C
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 50658
Re: A store sells a certain product at a fixed price per unit. A  [#permalink]

Show Tags

New post 30 Dec 2014, 01:04
edsafari wrote:
A store sells a certain product at a fixed price per unit. At the product's current price, q units cost a total of exactly $300. If the price were lowered by $5 from its current value, then q + 2n units would cost exactly $300; if the price were raised by $5, then q – n units would cost exactly $300. What is the value of q?

a: 10 b: 15 c: 20 d: 25 e: 30

in the solution, they say, this problem is to hard to solve with algebra, so they just put in the answer choices and figure out what ist right... That is ok for me, but I don't get how you can se if a problem of this kind is solvable quickly or if it is better just to go with the answer options. Has anybody an advice about that? The problem above didn't look that hard for me so I spent 2 min with it and got the wrong answer:)


Merging topics. Please refer to the discussion on page 1.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

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.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

GMAT Club Bot
Re: A store sells a certain product at a fixed price per unit. A &nbs [#permalink] 30 Dec 2014, 01:04

Go to page    1   2    Next  [ 26 posts ] 

Display posts from previous: Sort by

A store sells a certain product at a fixed price per unit. A

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


cron
Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.