Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 28 Jun 2016, 19:21

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# What does p equal?

Author Message
TAGS:

### Hide Tags

Manager
Joined: 16 Jan 2011
Posts: 103
Followers: 11

Kudos [?]: 125 [2] , given: 13

### Show Tags

25 Jun 2012, 11:57
2
KUDOS
2
This post was
BOOKMARKED
00:00

Difficulty:

55% (hard)

Question Stats:

51% (02:06) correct 49% (01:09) wrong based on 128 sessions

### HideShow timer Statistics

What does p equal?

(1) $$2p^2=p^3$$

(2) $$p=2\sqrt{p-1}$$

i went with D, but was wrong

(1) 2p^2=p^3 divided by p^2 --> 2=p - here was the mistake and id like to ask you to shed the light on this - what don't i understand correctly here?
[Reveal] Spoiler: OA
Math Expert
Joined: 02 Sep 2009
Posts: 33547
Followers: 5944

Kudos [?]: 73760 [3] , given: 9903

### Show Tags

25 Jun 2012, 12:07
3
KUDOS
Expert's post
1
This post was
BOOKMARKED
Galiya wrote:
What does p equal?

(1) 2p^2=p^3
(2) p=2sqrt{p-1}

i went with D, but was wrong

(1) 2p^2=p^3 divided by p^2 --> 2=p - here was the mistake and id like to ask you to shed the light on this - what don't i understand correctly here?

What does p equal?

(1) 2p^2=p^3 --> $$p^3-2p^2=0$$ --> $$p^2(p-2)=0$$ --> $$p=0$$ or $$p=2$$. Not sufficient.

(2) $$p=2\sqrt{p-1}$$ --> $$p^2=4(p-1)$$ --> $$p^2-4p+4=0$$ --> $$(p-2)^2=0$$ --> $$p=2$$. Sufficient.

As for your solution: you cannot divide by $$p^2$$ since $$p$$ could be zero and division by zero is not allowed.

Never reduce equation by variable (or expression with variable), if you are not certain that variable (or expression with variable) doesn't equal to zero. We can not divide by zero. So, if you divide (reduce) by $$p^2$$ you assume, with no ground for it, that $$p$$ does not equal to zero thus exclude a possible solution.

Hope it's clear.
_________________
Manager
Joined: 16 Jan 2011
Posts: 103
Followers: 11

Kudos [?]: 125 [0], given: 13

Re: What does p equal? [#permalink]

### Show Tags

25 Jun 2012, 12:14
thank you, Bunuel!sometimes Im really stuck on such a silly things
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 10227
Followers: 482

Kudos [?]: 124 [0], given: 0

Re: What does p equal? [#permalink]

### Show Tags

30 Jun 2014, 07:39
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Intern
Joined: 05 Aug 2014
Posts: 34
Followers: 0

Kudos [?]: 35 [0], given: 24

### Show Tags

24 May 2015, 10:41
What does p equal?
1) 2p^2 = p^3
2) p = 2 sqrt (p-1)

Source: Optimus Prep

The way I thought about the first statement was to divide both sides by p^2; accordingly, I got p = 2. The explanation given, however, was as follows:
1. p^3 - 2p^2 = 0
2. p^2(p - 2) =0
3. p = 0 or p-2 =0
Therefore, p could be either 0 or 2.

Could anyone please explain why the way i went about the first statement was wrong?
Math Expert
Joined: 02 Sep 2009
Posts: 33547
Followers: 5944

Kudos [?]: 73760 [0], given: 9903

Re: What does p equal? [#permalink]

### Show Tags

24 May 2015, 10:44
Expert's post
naeln wrote:
What does p equal?
1) 2p^2 = p^3
2) p = 2 sqrt (p-1)

Source: Optimus Prep

The way I thought about the first statement was to divide both sides by p^2; accordingly, I got p = 2. The explanation given, however, was as follows:
1. p^3 - 2p^2 = 0
2. p^2(p - 2) =0
3. p = 0 or p-2 =0
Therefore, p could be either 0 or 2.

Could anyone please explain why the way i went about the first statement was wrong?

Merging topics.

Hope it helps.
_________________
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 6693
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Followers: 289

Kudos [?]: 1971 [0], given: 161

Re: What does p equal? [#permalink]

### Show Tags

24 May 2015, 11:23
Expert's post
Hi naeln,

You have to be careful when dividing by variables because you might accidentally REMOVE a potential solution to the equation.

Here's a simple example of that 'error':

How many solutions does the following equation have?

X^3 = X

Without too much trouble, you should realize that the solutions are...

[Reveal] Spoiler:
-1, 0 and 1

If you divide both sides by X though, you get....

X^2 = 1

Now the solutions are....

[Reveal] Spoiler:
-1 and 1. WHERE did the 0 go????? You divided it "out" when you divided both sides by X
.

Since each prompt requires that you properly deal with what you were given, you are responsible to find ALL of the potential answers. If you're thinking about dividing by a variable, then you might instead try factoring the equation first.

GMAT assassins aren't born, they're made,
Rich
_________________

# Rich Cohen

Co-Founder & GMAT Assassin

# Special Offer: Save \$75 + GMAT Club Tests

60-point improvement guarantee
www.empowergmat.com/

***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************

Re: What does p equal?   [#permalink] 24 May 2015, 11:23
Similar topics Replies Last post
Similar
Topics:
5 If pyramid P and rectangular box B are of equal height, what is the ra 6 28 Sep 2015, 04:27
3 If xy does not equal zero, what is the value of xy? 2 05 Nov 2014, 08:22
30 What does |2b| equal? 19 25 Jun 2012, 12:23
If x does not equal 0 what is the value of (x^p/x^q)^2 3 18 Apr 2012, 01:48
4 If (p - q) is not equal to zero, what is the value of p/(p - 3 15 Sep 2011, 06:25
Display posts from previous: Sort by

# What does p equal?

 Powered by phpBB © phpBB Group and phpBB SEO 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®.