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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

28 Feb 2012, 05:14

1

This post received KUDOS

4

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

55% (hard)

Question Stats:

62% (01:26) correct 38% (01:47) wrong based on 210 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

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.

Re: Permutations and Combinations Question!!! [#permalink]

Show Tags

28 Feb 2012, 05:31

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!

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

Re: Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

25 Mar 2013, 05:44

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..

Re: Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

03 May 2014, 07:57

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.
_________________

Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

23 Mar 2015, 07:35

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.
_________________

Thanks, Lucky

_______________________________________________________ Kindly press the to appreciate my post !!

Four persons enter a lift on the ground floor of a nine-floor 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 (Non-Event) =1 Where event =all leaving at different floors.

Please help me in finding solution by P(Event)= 1- P(Non-event)

Please explain how to calculate using the Non-Event method.

hi, why do you want it to become complicated by solving this by non-event. 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
_________________

Re: Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

23 Mar 2015, 11:12

chetan2u wrote:

samichange wrote:

Four persons enter a lift on the ground floor of a nine-floor 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 (Non-Event) =1 Where event =all leaving at different floors.

Please help me in finding solution by P(Event)= 1- P(Non-event)

Please explain how to calculate using the Non-Event method.

hi, why do you want it to become complicated by solving this by non-event. 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 non-event method and arrived at the correct answer. I found it little complicated to solve by the non-event method. Took me 30 minutes to solve by the non-event 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

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.
_________________

Re: Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

23 Mar 2015, 21:35

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.
_________________

Thanks, Lucky

_______________________________________________________ Kindly press the to appreciate my post !!

Re: Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

04 Aug 2015, 00:23

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

Re: Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

18 Aug 2017, 18:26

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.
_________________

Re: Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

18 Aug 2017, 19:18

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.

Concentration: General Management, Entrepreneurship

Re: Four persons enter the lift of a seven storey building at [#permalink]

Show Tags

19 Aug 2017, 10:28

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.