Last visit was: 07 Jun 2024, 05:54 It is currently 07 Jun 2024, 05:54
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
SORT BY:
Date
Tags:
Show Tags
Hide Tags
avatar
Intern
Intern
Joined: 30 Jan 2010
Posts: 10
Own Kudos [?]: 9 [8]
Given Kudos: 1
Send PM
Most Helpful Reply
Math Expert
Joined: 02 Sep 2009
Posts: 93591
Own Kudos [?]: 629784 [10]
Given Kudos: 82179
Send PM
General Discussion
SVP
SVP
Joined: 17 Nov 2007
Posts: 2406
Own Kudos [?]: 10082 [1]
Given Kudos: 361
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Send PM
avatar
Intern
Intern
Joined: 30 Jan 2010
Posts: 10
Own Kudos [?]: 9 [0]
Given Kudos: 1
Send PM
Re: Premutations and Combinations [#permalink]
Thanks walker!

I already checked the other problem, the thing is: if I use the same approach, the answer I get is 480... I really can't seem to understand WHY I should divide 6! in 2 and then 5! also.
avatar
Intern
Intern
Joined: 30 Jan 2010
Posts: 10
Own Kudos [?]: 9 [0]
Given Kudos: 1
Send PM
Re: Premutations and Combinations [#permalink]
Walker...

Tell me if I'm right

The total combination is 6! = 720
The total combination of E1 and E2 together is 5! = 120

720 - 120 = 600... BUT since they're only asking for one E, then 600/2 = 300

Am I reasoning this OK?
SVP
SVP
Joined: 17 Nov 2007
Posts: 2406
Own Kudos [?]: 10082 [0]
Given Kudos: 361
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Send PM
Re: Premutations and Combinations [#permalink]
Expert Reply
pclg wrote:
Am I reasoning this OK?

Yeah, you are right.
User avatar
Manager
Manager
Joined: 22 Dec 2009
Posts: 179
Own Kudos [?]: 952 [2]
Given Kudos: 48
Send PM
Re: Premutations and Combinations [#permalink]
2
Kudos
walker wrote:
REVIEW

1) All arrangements: 6!/2 = 360 (1/2 in order to exclude double counting as [E1, E2] is the same as [E2,E1])
2) All arrangements with two E together: 5!/2 = 60
3) All arrangements in which one E can't be next to the other: 360 - 60 = 300.

By the way, look at this problem: permutation-sitting-arrangement-90121.html
it tests the same concept.


Hi Walker / Bunuel..... I do not understand why do we divide the All E arrangements by 2

We are already considering both the E as one single component... and therefore to arrange 5 different letters - R-E1E2-V-I-W... is 5!.... I guess this number of arrangement do not include both cases like R-E1E2-V-I-W & R-E2E1-V-I-W... as we haven't multiplied 5! with 2!(ways in which E1&E2 can be arranged between themselves). Hence I don't see the need to divide 5! by 2....

Can you please let me know if my reasoning is wrong?

As per the answer should be: 6!/2! (as this arrangement as 2 duplicate E) - 5! (as duplicate E is no more concern since they are one single unit for us) = 240!
User avatar
Manager
Manager
Joined: 22 Dec 2009
Posts: 179
Own Kudos [?]: 952 [0]
Given Kudos: 48
Send PM
Re: Premutations and Combinations [#permalink]
Bunuel wrote:
jeeteshsingh wrote:
walker wrote:
REVIEW

1) All arrangements: 6!/2 = 360 (1/2 in order to exclude double counting as [E1, E2] is the same as [E2,E1])
2) All arrangements with two E together: 5!/2 = 60
3) All arrangements in which one E can't be next to the other: 360 - 60 = 300.

By the way, look at this problem: permutation-sitting-arrangement-90121.html
it tests the same concept.


Hi Walker / Bunuel..... I do not understand why do we divide the All E arrangements by 2

We are already considering both the E as one single component... and therefore to arrange 5 different letters - R-E1E2-V-I-W... is 5!.... I guess this number of arrangement do not include both cases like R-E1E2-V-I-W & R-E2E1-V-I-W... as we haven't multiplied 5! with 2!(ways in which E1&E2 can be arranged between themselves). Hence I don't see the need to divide 5! by 2....

Can you please let me know if my reasoning is wrong?

As per the answer should be: 6!/2! (as this arrangement as 2 duplicate E) - 5! (as duplicate E is no more concern since they are one single unit for us) = 240!

THEORY:

Permutations of n things of which P1 are alike of one kind, P2 are alike of second kind, P3 are alike of third kind ...................... Pr are alike of r th kind such that: P1+P2+P3+..+Pr=n is:

\(\frac{n!}{P1!*P2!*P3!*...*Pr!}\).

For example number of permutation of the letters of the word "gmatclub" is 8! as there are 8 DISTINCT letters in this word.

Number of permutation of the letters of the word "google" is 6!/2!2!, as there are 6 letters out of which "g" and "o" are represented twice.

Number of permutation of 9 balls out of which 4 are red, 3 green and 2 blue, would be 9!/4!3!2!.


In the original question there are 6 letters out of which E appears twice. Total number of permutation of these letters (without restriction) would be: \(\frac{6!}{2!}=360\).

# of combination for which two E are adjacent is \(5!=120\), (consider two E as one element like: {R}{EE}{V}{I}{W}: # of permutation of this 5 elements is \(5!=120\))

Total # of permutation for which two E are not adjacent would be \(360-120=240\).

So yes, I think you are right.


Thanks Bunuel.... but I doubt Walker goes wrong on Permutation & Combinations! Walker is quite good in this topic! I hope I see the same confirmation coming from her side!
SVP
SVP
Joined: 17 Nov 2007
Posts: 2406
Own Kudos [?]: 10082 [0]
Given Kudos: 361
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Send PM
Re: Premutations and Combinations [#permalink]
Expert Reply
jeeteshsingh wrote:
Thanks Bunuel.... but I doubt Walker goes wrong on Permutation & Combinations! Walker is quite good in this topic! I hope I see the same confirmation coming from her side!


Jeeteshsingh, from "his side" :wink: Yeah, you are absolutely right.
User avatar
Manager
Manager
Joined: 22 Dec 2009
Posts: 179
Own Kudos [?]: 952 [0]
Given Kudos: 48
Send PM
Re: Premutations and Combinations [#permalink]
walker wrote:
jeeteshsingh wrote:
Thanks Bunuel.... but I doubt Walker goes wrong on Permutation & Combinations! Walker is quite good in this topic! I hope I see the same confirmation coming from her side!


Jeeteshsingh, from "his side" :wink: Yeah, you are absolutely right.


Hahaha! My apologises Mate!!! HIS SIDE!!! :)
SVP
SVP
Joined: 17 Nov 2007
Posts: 2406
Own Kudos [?]: 10082 [2]
Given Kudos: 361
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Send PM
Re: Premutations and Combinations [#permalink]
2
Kudos
Expert Reply
jeeteshsingh wrote:
Hahaha! My apologises Mate!!! HIS SIDE!!! :)


Do you often see a woman riding a bike and developing iPhone Apps? :shock: :lol:
User avatar
Manager
Manager
Joined: 22 Dec 2009
Posts: 179
Own Kudos [?]: 952 [0]
Given Kudos: 48
Send PM
Re: Premutations and Combinations [#permalink]
walker wrote:

Do you often see a woman riding a bike and developing iPhone Apps? :shock: :lol:


Riding bikes is not that big a thing... but yeh... iphones apps... yeh its hard to believe...

All this while I was on the right track... unless recently I saw some of the old fourm topics and I read somewhere.. that u r a girl from Ukraine! lol! :D

No worries.. glad it's all clear now!!! ;)
User avatar
Manager
Manager
Joined: 01 Feb 2010
Posts: 90
Own Kudos [?]: 136 [0]
Given Kudos: 2
Send PM
Re: Premutations and Combinations [#permalink]
pclg wrote:
Possible arrangements for the word REVIEW if one E can't be next to the other.

I just can't find the answer!


Total ways = 6!/2! = 360
When both E's together = 5! = 120

Answer = 360 - 120 = 240
User avatar
Manager
Manager
Joined: 16 Jun 2010
Posts: 101
Own Kudos [?]: 551 [1]
Given Kudos: 5
Send PM
Re: Premutations and Combinations [#permalink]
1
Bookmarks
I solved it a bit differently;

Here my Approach goes:
1. ExEyyy
Above, P(x) = 4C1 = 4.
Taking ExE as 1 term along with the 3 Y's we have 4 terms that can be arranged in 4! = 24 ways.
Hence the total possible combinations is: 4C1 * 4! * 1! = 96

2. ExxEyy -> 4C2 * 3! * 2! = 72
3. ExxxEy -> 4C3 * 2! * 3! = 48
4. ExxxxE -> 4C4 * 4! * 1! = 24

So adding up all together -> 240
avatar
Intern
Intern
Joined: 15 Jul 2013
Posts: 3
Own Kudos [?]: [0]
Given Kudos: 0
Schools: Booth PT '19
Send PM
Re: Possible arrangements for the word REVIEW if one E can't be [#permalink]
Hi,
Just wanted to check why the answer is not 120

Review : 6 letters, 2 common = 6*5*4*3 = 360
Case where 2 Es are glued together = 5!*2 (2 as either of the two Es could come first)
= 360 - 240
= 120
what am I missing
Math Expert
Joined: 02 Sep 2009
Posts: 93591
Own Kudos [?]: 629784 [0]
Given Kudos: 82179
Send PM
Re: Possible arrangements for the word REVIEW if one E can't be [#permalink]
Expert Reply
adeel2000 wrote:
Hi,
Just wanted to check why the answer is not 120

Review : 6 letters, 2 common = 6*5*4*3 = 360
Case where 2 Es are glued together = 5!*2 (2 as either of the two Es could come first)
= 360 - 240
= 120
what am I missing


Two E's can be arranged only one way: EE.
Manager
Manager
Joined: 11 Jun 2017
Posts: 55
Own Kudos [?]: 102 [0]
Given Kudos: 8
Send PM
Re: Possible arrangements for the word REVIEW if one E can't be [#permalink]
Hi Bunuel,

Please let me know if my approach is correct.

Taking different conditions where one letter is between the two "E"s, then a condition where two letters are between the two "E"s, then 3 and then finally 4 between the two "E".
Total combinations= 4C1*4!+ 4C2*2*3!+4C3*3!*2+4C4*4!
= 96+72+48+24 = 240.
VP
VP
Joined: 11 Aug 2020
Posts: 1257
Own Kudos [?]: 204 [0]
Given Kudos: 332
Send PM
Re: Possible arrangements for the word REVIEW if one E can't be [#permalink]
Do we have the answer choices in the OP?

Answer should be 240.

Permutations without restrictions: 6!/2! = 360
# of ways E are both together = 5! / (5-5)! = 120

360 - 120 = 240
User avatar
Non-Human User
Joined: 09 Sep 2013
Posts: 33366
Own Kudos [?]: 833 [0]
Given Kudos: 0
Send PM
Re: Possible arrangements for the word REVIEW if one E can't be [#permalink]
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.
GMAT Club Bot
Re: Possible arrangements for the word REVIEW if one E can't be [#permalink]
Moderator:
Math Expert
93591 posts