Processing math: 100%

Last visit was: 11 Apr 2025, 09:58 It is currently 11 Apr 2025, 09:58
Decision Tracker
My Rewards
New comers' posts
New posts
Unanswered

Close

GRE Prep 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 GRE 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.

Go to My Error Log Learn more
Close

Request Expert Reply

Confirm Cancel
PREVIOUS TOPIC
NEXT TOPIC

There are 12 floors in a building and 10 persons are about to leave

Tags :
Find Similar Topics  About  Add a Tag

Show Tags
Hide Tags

User avatar
D
KarunMendiratta
Retired Moderator
Joined: 16 Apr 2020
Status:Founder & Quant Trainer
Affiliations: Prepster Education
Posts: 1546
Own Kudos [?]: 3345 [19]
Given Kudos: 172
Location: India
WE:Education (Education)
Send PM
There are 12 floors in a building and 10 persons are about to leave [#permalink] New post   06 Mar 2021, 04:42
2
1
16
Bookmarks
00:00
A
B
C
D

Question Stats:

60% (02:07) correct 39% (02:05) wrong based on 28 sessions

Show timer Statistics

There are 12 floors in a building and 10 persons are about to leave a lift. Exactly 3 among them would leave at 5th floor.

Quantity A
Quantity B
Number of ways they can leave the lift
2.4 x 109


(A) Quantity A is greater
(B) Quantity B is greater
(C) The two quantities are equal
(D) The relationship cannot be determined from the information given
ShowHide Answer
Official Answer
B
User avatar
D
KarunMendiratta
Retired Moderator
Joined: 16 Apr 2020
Status:Founder & Quant Trainer
Affiliations: Prepster Education
Posts: 1546
Own Kudos [?]: 3345 [3]
Given Kudos: 172
Location: India
WE:Education (Education)
Send PM
There are 12 floors in a building and 10 persons are about to leave [#permalink] New post   06 Mar 2021, 23:40
2
1
Bookmarks
OA Explanation

(5th 5th 5th) _ _ _ _ _ _ _

Since, there are 10 people and exactly 3 get down on 5th floor, there are 10C3 ways in which we can choose 3 people out of 10 for the same i.e. 120 ways

Now, rest 7 will have only 11 floor options, they can get down in 11 x 11 x 11 x 11 x 11 x 11 x 11 ways i.e. 117 ways

Col. A: 120 x 117
Col. B: 2.4 x 109

Col. A: 120 x 117
Col. B: 240 x 107

Dividing both sides by 120;

Col. A: 117
Col. B: 2 x 107

Dividing both sides by 107;

Col. A: (1110)7
Col. B: 2

Col. A: (1.10)7
Col. B: 2

Clearly, Col. A < Col. B

Hence, option B
avatar
S
void
Senior Manager
Senior Manager
Joined: 03 Dec 2020
Posts: 440
Own Kudos [?]: 62 [0]
Given Kudos: 68
Send PM
Re: There are 12 floors in a building and 10 persons are about to leave [#permalink] New post   11 Mar 2021, 02:31
question is hard or am i stupid?
User avatar
D
KarunMendiratta
Retired Moderator
Joined: 16 Apr 2020
Status:Founder & Quant Trainer
Affiliations: Prepster Education
Posts: 1546
Own Kudos [?]: 3345 [1]
Given Kudos: 172
Location: India
WE:Education (Education)
Send PM
Re: There are 12 floors in a building and 10 persons are about to leave [#permalink] New post   11 Mar 2021, 02:45
1
void wrote:
question is hard or am i stupid?


It is hand. On GRE it would be somewhere around 165+
avatar
S
nurakib
Manager
Manager
Joined: 22 Sep 2020
Posts: 74
Own Kudos [?]: 67 [0]
Given Kudos: 97
Send PM
There are 12 floors in a building and 10 persons are about to leave [#permalink] New post   16 Mar 2021, 12:48
KarunMendiratta wrote:
OA Explanation

(5th 5th 5th) _ _ _ _ _ _ _

Since, there are 10 people and exactly 3 get down on 5th floor, there are 10C2 ways in which we can choose 3 people out of 10 for the same i.e. 120 ways

Now, rest 7 will have only 11 floor options, they can get down in 11 x 11 x 11 x 11 x 11 x 11 x 11 ways i.e. 117 ways

Col. A: 120 x 117
Col. B: 2.4 x 109

Col. A: 120 x 117
Col. B: 240 x 107

Dividing both sides by 120;

Col. A: 117
Col. B: 2 x 107

Dividing both sides by 107;

Col. A: (1110)7
Col. B: 2

Col. A: (1.10)7
Col. B: 2

Clearly, Col. A < Col. B

Hence, option B


Quote:
Since, there are 10 people and exactly 3 get down on 5th floor, there are 10C2 ways in which we can choose 3 people out of 10 for the same i.e. 120 ways


why it is not 10C3? I don't understand it.
User avatar
D
KarunMendiratta
Retired Moderator
Joined: 16 Apr 2020
Status:Founder & Quant Trainer
Affiliations: Prepster Education
Posts: 1546
Own Kudos [?]: 3345 [0]
Given Kudos: 172
Location: India
WE:Education (Education)
Send PM
There are 12 floors in a building and 10 persons are about to leave [#permalink] New post   16 Mar 2021, 20:26
nurakib wrote:
KarunMendiratta wrote:
OA Explanation

(5th 5th 5th) _ _ _ _ _ _ _

Since, there are 10 people and exactly 3 get down on 5th floor, there are 10C2 ways in which we can choose 3 people out of 10 for the same i.e. 120 ways

Now, rest 7 will have only 11 floor options, they can get down in 11 x 11 x 11 x 11 x 11 x 11 x 11 ways i.e. 117 ways

Col. A: 120 x 117
Col. B: 2.4 x 109

Col. A: 120 x 117
Col. B: 240 x 107

Dividing both sides by 120;

Col. A: 117
Col. B: 2 x 107

Dividing both sides by 107;

Col. A: (1110)7
Col. B: 2

Col. A: (1.10)7
Col. B: 2

Clearly, Col. A < Col. B

Hence, option B


Quote:
Since, there are 10 people and exactly 3 get down on 5th floor, there are 10C2 ways in which we can choose 3 people out of 10 for the same i.e. 120 ways


why it is not 10C3? I don't understand it.


It is 10C3 only, I have edited the explanation. Thanks!
avatar
B
cote
Intern
Intern
Joined: 11 Aug 2020
Posts: 45
Own Kudos [?]: 76 [0]
Given Kudos: 17
Send PM
Re: There are 12 floors in a building and 10 persons are about to leave [#permalink] New post   22 Sep 2022, 12:00
KarunMendiratta wrote:
OA Explanation

(5th 5th 5th) _ _ _ _ _ _ _

Since, there are 10 people and exactly 3 get down on 5th floor, there are 10C3 ways in which we can choose 3 people out of 10 for the same i.e. 120 ways

Now, rest 7 will have only 11 floor options, they can get down in 11 x 11 x 11 x 11 x 11 x 11 x 11 ways i.e. 117 ways

Col. A: 120 x 117
Col. B: 2.4 x 109

Col. A: 120 x 117
Col. B: 240 x 107

Dividing both sides by 120;

Col. A: 117
Col. B: 2 x 107

Dividing both sides by 107;

Col. A: (1110)7
Col. B: 2

Col. A: (1.10)7
Col. B: 2

Clearly, Col. A < Col. B

Hence, option B


I have a little uestion here:

why are we calculating 10C3 instead of 10P3?.

My reasoning is the following,

lets say that every person is labeled with a letter: (A,B,C..). Because order matters, we have to count the order in which the group get down from the lift

Person | floor
A | 1
B | 2
C | 3
D | 4
E | 5
F | 5
G | 5
H | 8
J | 9
K | 10

in this case, person E, F and G got down on the 5th floor (in that order). However, we could also have this case:


Person | floor
A | 1
B | 2
C | 3
D | 4
F | 5
E | 5
G | 5
H | 8
J | 9
K | 10

In this situation, person F got down first, followed by E and G, which is clearly a different combination, which in my opinion, is not captured by 10C3.

am I mistaken?,

Thanks!!
User avatar
bumpbot
GRE Prep Club Legend
GRE Prep Club Legend
Joined: 07 Jan 2021
Posts: 5244
Own Kudos [?]: 77 [0]
Given Kudos: 0
Send PM
Re: There are 12 floors in a building and 10 persons are about to leave [#permalink] New post   07 Dec 2023, 22:56
Hello from the GRE Prep Club BumpBot!

Thanks to another GRE Prep 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.
Prep Club for GRE Bot
gmatclubot
Re: There are 12 floors in a building and 10 persons are about to leave [#permalink]
07 Dec 2023, 22:56
Moderators:
adewale223
GRE Instructor
108 posts
bronaugust
GRE Forum Moderator
37 posts
BrushMyQuant
Moderator
1131 posts
VibhuAnurag
GRE Instructor
234 posts

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

Main navigation

Partners

GRE Resources

www.ets.org/gre | About | Terms and Conditions and Privacy Policy | Prep Club for GRE Rules | Contact