Apr 20 07:00 AM PDT  09:00 AM PDT Christina scored 760 by having clear (ability) milestones and a trackable plan to achieve the same. Attend this webinar to learn how to build trackable milestones that leverage your strengths to help you get to your target GMAT score. Apr 20 10:00 PM PDT  11:00 PM PDT The Easter Bunny brings … the first day of school?? Yes! Now is the time to start studying for the GMAT if you’re planning to apply to Round 1 of fall MBA programs. Get a special discount with the Easter sale! Apr 21 07:00 AM PDT  09:00 AM PDT Get personalized insights on how to achieve your Target Quant Score. Apr 21 10:00 PM PDT  11:00 PM PDT $84 + an extra $10 off for the first month of EMPOWERgmat access. Train to be ready for Round 3 Deadlines with EMPOWERgmat's Score Booster. Ends April 21st Code: GCENHANCED Apr 22 08:00 AM PDT  09:00 AM PDT 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. Save your spot today! Apr 23 08:00 PM EDT  09:00 PM EDT Strategies and techniques for approaching featured GMAT topics. Tuesday, April 23rd at 8 pm ET Apr 24 08:00 PM EDT  09:00 PM EDT Maximize Your Potential: 5 Steps to Getting Your Dream MBA Part 3 of 5: Key TestTaking Strategies for GMAT. Wednesday, April 24th at 8 pm ET
Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 19 Feb 2012
Posts: 4

Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
28 Feb 2012, 06:14
Question Stats:
60% (01:54) correct 40% (01:55) wrong based on 220 sessions
HideShow timer Statistics
Four persons enter the lift of a seven storey building at the ground floor. In how many ways can they get out of lift on any floor other than ground floor A. 720 B. 1296 C. 1540 D. 1478 E. 360
Official Answer and Stats are available only to registered users. Register/ Login.




Math Expert
Joined: 02 Sep 2009
Posts: 54369

Re: Permutations and Combinations Question!!!
[#permalink]
Show Tags
28 Feb 2012, 06:22
kiran882 wrote: Four persons enter the lift of a seven storey building at the ground floor. In how many ways can they get out of lift on any floor other than ground floor
A. 720 B. 1296 C. 1540 D. 1478 E. 360 Welcome to GMAT Club. Below is a solution to your question. Each person out of 4 has 6 floors (options) to get out of (since no one gets out on the ground floor), hence total ways is 6*6*6*6=6^4. Now, there is no need to actually calculate this value: 6^4 will have 6 as the units digit and there is only one option (B) which offers such a number. Answer: B. Hope it's clear.
_________________




Intern
Joined: 19 Feb 2012
Posts: 4

Re: Permutations and Combinations Question!!!
[#permalink]
Show Tags
28 Feb 2012, 06:31
Bunuel wrote: kiran882 wrote: Four persons enter the lift of a seven storey building at the ground floor. In how many ways can they get out of lift on any floor other than ground floor
A. 720 B. 1296 C. 1540 D. 1478 E. 360 Welcome to GMAT Club. Below is a solution to your question. Each person out of 4 has 6 floors (options) to get out of (since no one gets out on the ground floor), hence total ways is 6*6*6*6=6^4. Now, there is no need to actually calculate this value: 6^4 will have 6 as the units digit and there is only one option (B) which offers such a number. Answer: B. Hope it's clear. Oh!! Its very easy question! Thanks for ur lucid explanation!



Manager
Status: Do till 740 :)
Joined: 13 Jun 2011
Posts: 84
Concentration: Strategy, General Management
GPA: 3.6
WE: Consulting (Computer Software)

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
14 Apr 2012, 20:33
Hi Buneul,
When they say 4 and 6 floors should we not account the possibility that
1st floor : A
2 nd floor B
3rd floor C 4th floor D
alos combinations like
1st floor AB
or BC
Am i confused?



Math Expert
Joined: 02 Sep 2009
Posts: 54369

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
15 Apr 2012, 00:24
shankar245 wrote: Hi Buneul,
When they say 4 and 6 floors should we not account the possibility that
1st floor : A
2 nd floor B
3rd floor C 4th floor D
alos combinations like
1st floor AB
or BC
Am i confused? Try to consider simpler example (3 floors, 2 persons) and see whether the cases when both of them get out on the same floor are counted in 3^2. You'll see that they are: I  II  III (Floors) A  B B  A A  *  B B  *  A *  A  B *  B  A AB *  AB *  *  AB Hope it helps.
_________________



Intern
Joined: 20 Nov 2012
Posts: 15

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
25 Mar 2013, 06:44
Hi Brunel,
I tried a different approach which I thought would also be applicable in this situation but got a different answer. Can you please tell me where did I go wrong? Here we go:
Option 1: All 4 people get out on one of the six floors. This can be done in 6 ways (2nd floor, 3rd floor, 4th floor, etc)
Option 2: 3 people get out together on one floor, and I person on a different floor. This can be done in the following manner: 4C3 * 1C1 * 6!/4! = 120 ways
Option 3: 2 people get out on one floor and 2 on another floor: 4C2 * 2C2 * 6!/4! = 180 ways
Option 4: 2 people get out on one floor and then 1 and 1. Again we have
4C2 * 6!/3! = 720 ways
Option 5: One person on each floor:
6!/2! = 360 ways
A total of 1386 ways. But my answers is different than yours..



Director
Joined: 07 Aug 2011
Posts: 523
Concentration: International Business, Technology

Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
23 Mar 2015, 08:35
kiran882 wrote: Four persons enter the lift of a seven storey building at the ground floor. In how many ways can they get out of lift on any floor other than ground floor
A. 720 B. 1296 C. 1540 D. 1478 E. 360 Just want to check one doubt regarding ground floor, does it represents floor# 0 OR Floor# 1 ? The country where i live ground floor represents 0 , and with that in mind i was trying 7*7*7*7 , none of the option has 1 as unit digit so i inferred that ground floor here represents floor #1 . are we expected to have such knowledge specific to a country ? for eg: 1 have one permutation/combination question QU: A family of 5 is going for a summer vacation and they decided to drive the car (with 5 seats ) to a hill station . family is composed of 2 daughters ,1 son and parents. only parents can drive . none of the girl want to sit adjacent to a right side window of the car. how many possible combinations are there ? considering in USA the steering is on left side while in ASIA the steering in on right side , we will have two different answers for this question.



Math Expert
Joined: 02 Aug 2009
Posts: 7556

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
23 Mar 2015, 09:13
samichange wrote: Four persons enter a lift on the ground floor of a ninefloor building. Each person is equally likely to leave the lift at any floor except the ground floor. What is the probability of all the persons leaving the lift at different floors?
A. 105/512 B. 105/256 C. 112/243 D. 1560/2147 E. 7/8
I have solved the above; but I have a doubt. P(Event) + P (NonEvent) =1 Where event =all leaving at different floors.
Please help me in finding solution by P(Event)= 1 P(Nonevent)
Please explain how to calculate using the NonEvent method. hi, why do you want it to become complicated by solving this by nonevent. rather if it asks you for probability of people not leaving on different floors, you would use non event method.. choose this method when it simplifies calculations example.. atleast one thing is done.. etc
_________________



Senior Manager
Joined: 01 Nov 2013
Posts: 289
WE: General Management (Energy and Utilities)

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
23 Mar 2015, 12:12
chetan2u wrote: samichange wrote: Four persons enter a lift on the ground floor of a ninefloor building. Each person is equally likely to leave the lift at any floor except the ground floor. What is the probability of all the persons leaving the lift at different floors?
A. 105/512 B. 105/256 C. 112/243 D. 1560/2147 E. 7/8
I have solved the above; but I have a doubt. P(Event) + P (NonEvent) =1 Where event =all leaving at different floors.
Please help me in finding solution by P(Event)= 1 P(Nonevent)
Please explain how to calculate using the NonEvent method. hi, why do you want it to become complicated by solving this by nonevent. rather if it asks you for probability of people not leaving on different floors, you would use non event method.. choose this method when it simplifies calculations example.. atleast one thing is done.. etc Hi Thanks. I just solved it little while ago by the nonevent method and arrived at the correct answer. I found it little complicated to solve by the nonevent method. Took me 30 minutes to solve by the nonevent method.
_________________
Our greatest weakness lies in giving up. The most certain way to succeed is always to try just one more time.
I hated every minute of training, but I said, 'Don't quit. Suffer now and live the rest of your life as a champion.Mohammad Ali



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9119
Location: Pune, India

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
23 Mar 2015, 22:07
Lucky2783 wrote: kiran882 wrote: Four persons enter the lift of a seven storey building at the ground floor. In how many ways can they get out of lift on any floor other than ground floor
A. 720 B. 1296 C. 1540 D. 1478 E. 360 Just want to check one doubt regarding ground floor, does it represents floor# 0 OR Floor# 1 ? The country where i live ground floor represents 0 , and with that in mind i was trying 7*7*7*7 , none of the option has 1 as unit digit so i inferred that ground floor here represents floor #1 . are we expected to have such knowledge specific to a country ? for eg: 1 have one permutation/combination question QU: A family of 5 is going for a summer vacation and they decided to drive the car (with 5 seats ) to a hill station . family is composed of 2 daughters ,1 son and parents. only parents can drive . none of the girl want to sit adjacent to a right side window of the car. how many possible combinations are there ? considering in USA the steering is on left side while in ASIA the steering in on right side , we will have two different answers for this question. A seven storey building means a building with seven floors  it doesn't matter how you name them. You could call them "floor 1 to floor 7" or "ground floor to floor 6". If the seven storey building has a ground floor (as given in the question), it will have 6 more floors above it. So either ways, your answer will be the same irrespective of the country to which you belong. As for the car question, you will not see such a discrepancy in an actual GMAT question.
_________________
Karishma Veritas Prep GMAT Instructor
Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >



Director
Joined: 07 Aug 2011
Posts: 523
Concentration: International Business, Technology

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
23 Mar 2015, 22:35
VeritasPrepKarishma wrote: Lucky2783 wrote: kiran882 wrote: Four persons enter the lift of a seven storey building at the ground floor. In how many ways can they get out of lift on any floor other than ground floor
A. 720 B. 1296 C. 1540 D. 1478 E. 360 Just want to check one doubt regarding ground floor, does it represents floor# 0 OR Floor# 1 ? The country where i live ground floor represents 0 , and with that in mind i was trying 7*7*7*7 , none of the option has 1 as unit digit so i inferred that ground floor here represents floor #1 . are we expected to have such knowledge specific to a country ? for eg: 1 have one permutation/combination question QU: A family of 5 is going for a summer vacation and they decided to drive the car (with 5 seats ) to a hill station . family is composed of 2 daughters ,1 son and parents. only parents can drive . none of the girl want to sit adjacent to a right side window of the car. how many possible combinations are there ? considering in USA the steering is on left side while in ASIA the steering in on right side , we will have two different answers for this question. A seven storey building means a building with seven floors  it doesn't matter how you name them. You could call them "floor 1 to floor 7" or "ground floor to floor 6". If the seven storey building has a ground floor (as given in the question), it will have 6 more floors above it. So either ways, your answer will be the same irrespective of the country to which you belong. As for the car question, you will not see such a discrepancy in an actual GMAT question. thank you karishma for the clarifications.



Manager
Joined: 03 May 2013
Posts: 67

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
04 Aug 2015, 01:23
kiran882 wrote: Bunuel wrote: kiran882 wrote: Four persons enter the lift of a seven storey building at the ground floor. In how many ways can they get out of lift on any floor other than ground floor
A. 720 B. 1296 C. 1540 D. 1478 E. 360 Hi Bunuel, I got the OE however Please let me know where i am wrong in this , No of ways for 1st floor to get persons = 5(0,1,2,3,4)similarly for all other floors , so i got 5^6



Manager
Joined: 27 Jun 2015
Posts: 61
WE: Information Technology (Computer Software)

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
18 Aug 2017, 20:18
Bunuel wrote: kiran882 wrote: Four persons enter the lift of a seven storey building at the ground floor. In how many ways can they get out of lift on any floor other than ground floor
A. 720 B. 1296 C. 1540 D. 1478 E. 360 Welcome to GMAT Club. Below is a solution to your question. Each person out of 4 has 6 floors (options) to get out of (since no one gets out on the ground floor), hence total ways is 6*6*6*6=6^4. Now, there is no need to actually calculate this value: 6^4 will have 6 as the units digit and there is only one option (B) which offers such a number. Answer: B. Hope it's clear. Hi Bunuel, Can you please tell me why can't we take it this way:4 can be out on 1st flr, 4 can be out on 2nd flr.. so effectively it will 4^6?



Intern
Joined: 25 Jan 2013
Posts: 28
Location: United States
Concentration: General Management, Entrepreneurship

Re: Four persons enter the lift of a seven storey building at
[#permalink]
Show Tags
19 Aug 2017, 11:28
kkrrsshh wrote: Bunuel wrote: kiran882 wrote: Four persons enter the lift of a seven storey building at the ground floor. In how many ways can they get out of lift on any floor other than ground floor
A. 720 B. 1296 C. 1540 D. 1478 E. 360 Welcome to GMAT Club. Below is a solution to your question. Each person out of 4 has 6 floors (options) to get out of (since no one gets out on the ground floor), hence total ways is 6*6*6*6=6^4. Now, there is no need to actually calculate this value: 6^4 will have 6 as the units digit and there is only one option (B) which offers such a number. Answer: B. Hope it's clear. Hi Bunuel, Can you please tell me why can't we take it this way:4 can be out on 1st flr, 4 can be out on 2nd flr.. so effectively it will 4^6? Each person has 6 floor option to choose from: 1: 6 option 2: 6 option etc .. 4 person so 6^4




Re: Four persons enter the lift of a seven storey building at
[#permalink]
19 Aug 2017, 11:28






