Last visit was: 19 Nov 2025, 11:01 It is currently 19 Nov 2025, 11:01
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
505-555 Level|   Number Properties|                  
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,390
Own Kudos:
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,390
Kudos: 778,308
 [45]
4
Kudos
Add Kudos
39
Bookmarks
Bookmark this Post
Most Helpful Reply
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,390
Own Kudos:
778,308
 [9]
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,390
Kudos: 778,308
 [9]
2
Kudos
Add Kudos
7
Bookmarks
Bookmark this Post
General Discussion
User avatar
fameatop
Joined: 24 Aug 2009
Last visit: 09 Jun 2017
Posts: 383
Own Kudos:
2,495
 [4]
Given Kudos: 275
Concentration: Finance
Schools:Harvard, Columbia, Stern, Booth, LSB,
Posts: 383
Kudos: 2,495
 [4]
1
Kudos
Add Kudos
3
Bookmarks
Bookmark this Post
User avatar
nelz007
Joined: 21 Sep 2012
Last visit: 16 Aug 2020
Posts: 178
Own Kudos:
1,488
 [4]
Given Kudos: 63
Posts: 178
Kudos: 1,488
 [4]
3
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
statement 1

s=r+10

so basically the numbers we have are r,r+1,r+2,r+3,r+4,r+5,r+6,r+7,r+8,r+9,r+10( r+10 is S)

so there are 9 integers in between another way to solve would be s-r+1 = 10+1 = 11 total number of integers
since we need the numbers in between 11 - 2 ( the 2 numbers we subtract are r and s) hence we get 9

statement 2

there are 9 integers so we have a total of 11 integers at the moment.

s+1 - (r+1) + 1 = 11
s+1-r-1=10
s-r=10 which is same as statement 1 sufficient

so answer is D
User avatar
Vips0000
User avatar
Current Student
Joined: 15 Sep 2012
Last visit: 02 Feb 2016
Posts: 521
Own Kudos:
1,291
 [1]
Given Kudos: 23
Status:Done with formalities.. and back..
Location: India
Concentration: Strategy, General Management
Schools: Olin - Wash U - Class of 2015
WE:Information Technology (Computer Software)
Products:
Schools: Olin - Wash U - Class of 2015
Posts: 521
Kudos: 1,291
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
From statement 1,
s-r=10
Sufficient to conclude number that s is 9 integers after r.

Statment 2,
s+1 is 9 integers after r+1
or s is 9 integers after r (same as S1)
Sufficient.

Hence D

Bunuel
The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions Project

How many integers are there between, but not including, integers r and s ?

(1) s-r=10
(2) There are 9 integers between, but not including, r + 1 and s + 1.

Practice Questions
Question: 64
Page: 280
Difficulty: 600

GMAT Club is introducing a new project: The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions Project

Each week we'll be posting several questions from The Official Guide for GMAT® Review, 13th Edition and then after couple of days we'll provide Official Answer (OA) to them along with a solution.

We'll be glad if you participate in development of this project:
1. Please provide your solutions to the questions;
2. Please vote for the best solutions by pressing Kudos button;
3. Please vote for the questions themselves by pressing Kudos button;
4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

Thank you!
avatar
inportsmouthva
Joined: 13 Dec 2011
Last visit: 03 Aug 2013
Posts: 2
Posts: 2
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
SOLUTION

How many integers are there between, but not including, integers r and s ?

Notice that we are told that r and s are integers.

(1) s – r = 10 --> since r and s are integers and s – r = 10 then there will be 9 integers between them. For example take s=10 and r=0, then there are following integers between them: 1, 2, 3, 4, 5, 6, 7, 8, and 9. Sufficient.

(2) There are 9 integers between, but not including, r + 1 and s + 1 --> the distance between r and s is the same as the distance between r+1 and s+1, so if there are 9 integers between, but not including, r+1 and s+1 then there will be 9 integers between, but not including, r and s too. For example consider s+1=11 and r+1=1 (9 integers between them: 2, 3, 4, 5, 6, 7, 8, 9, and 10) --> s=10 and r=0 the same as above. Sufficient.

Answer: D.

Kudos points given to everyone with correct solution. Let me know if I missed someone.

I still do not understand how (1) is sufficient. My train of thought on it being insufficient is as follows with and example
s-r=10

12-2= 10 if s= 12 and r= 2 but the consecutive set could be consecutive multiples 2,4,6,8,10,12. There would only be 4 integer in between.
Do we just assume they are a consecutive set of integers?
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,390
Own Kudos:
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,390
Kudos: 778,308
Kudos
Add Kudos
Bookmarks
Bookmark this Post
inportsmouthva
Bunuel
SOLUTION

How many integers are there between, but not including, integers r and s ?

Notice that we are told that r and s are integers.

(1) s – r = 10 --> since r and s are integers and s – r = 10 then there will be 9 integers between them. For example take s=10 and r=0, then there are following integers between them: 1, 2, 3, 4, 5, 6, 7, 8, and 9. Sufficient.

(2) There are 9 integers between, but not including, r + 1 and s + 1 --> the distance between r and s is the same as the distance between r+1 and s+1, so if there are 9 integers between, but not including, r+1 and s+1 then there will be 9 integers between, but not including, r and s too. For example consider s+1=11 and r+1=1 (9 integers between them: 2, 3, 4, 5, 6, 7, 8, 9, and 10) --> s=10 and r=0 the same as above. Sufficient.

Answer: D.

Kudos points given to everyone with correct solution. Let me know if I missed someone.

I still do not understand how (1) is sufficient. My train of thought on it being insufficient is as follows with and example
s-r=10

12-2= 10 if s= 12 and r= 2 but the consecutive set could be consecutive multiples 2,4,6,8,10,12. There would only be 4 integer in between.
Do we just assume they are a consecutive set of integers?

Let me ask you a question: how many integers are there between, but not including, 2 and 12?
avatar
inportsmouthva
Joined: 13 Dec 2011
Last visit: 03 Aug 2013
Posts: 2
Posts: 2
Kudos: 0
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel


Let me ask you a question: how many integers are there between, but not including, 2 and 12?
BINGO- I get it now. The lights just went on. There are 9. The question specifically states how many integers between the two numbers. It does not mention intervals. The question states "integers between"
The good thing is that I am learning that I am sometimes reading way too much into a question, thinking it can not be this easy.
This is part of my learning "what to watch out for, and what kind of mistakes I am making"
Thanks so much for your help
User avatar
yezz
User avatar
Retired Moderator
Joined: 05 Jul 2006
Last visit: 26 Apr 2022
Posts: 833
Own Kudos:
Given Kudos: 49
Posts: 833
Kudos: 1,661
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
How many integers are there between, but not including, integers r and s ?

Notice that we are told that r and s are integers.

(1) s – r = 10 --> since r and s are integers and s – r = 10 then there will be 9 integers between them. For example take s=10 and r=0, then there are following integers between them: 1, 2, 3, 4, 5, 6, 7, 8, and 9. Sufficient.

(2) There are 9 integers between, but not including, r + 1 and s + 1 --> the distance between r and s is the same as the distance between r+1 and s+1, so if there are 9 integers between, but not including, r+1 and s+1 then there will be 9 integers between, but not including, r and s too. For example consider s+1=11 and r+1=1 (9 integers between them: 2, 3, 4, 5, 6, 7, 8, 9, and 10) --> s=10 and r=0 the same as above. Sufficient.

Answer: D.

Hope it's clear.

Hi Bunuel , if i am not mistaken , why are we assuming that r and s belongs to an evenly spaced set of integers ??
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,390
Own Kudos:
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,390
Kudos: 778,308
Kudos
Add Kudos
Bookmarks
Bookmark this Post
yezz
Bunuel
How many integers are there between, but not including, integers r and s ?

Notice that we are told that r and s are integers.

(1) s – r = 10 --> since r and s are integers and s – r = 10 then there will be 9 integers between them. For example take s=10 and r=0, then there are following integers between them: 1, 2, 3, 4, 5, 6, 7, 8, and 9. Sufficient.

(2) There are 9 integers between, but not including, r + 1 and s + 1 --> the distance between r and s is the same as the distance between r+1 and s+1, so if there are 9 integers between, but not including, r+1 and s+1 then there will be 9 integers between, but not including, r and s too. For example consider s+1=11 and r+1=1 (9 integers between them: 2, 3, 4, 5, 6, 7, 8, 9, and 10) --> s=10 and r=0 the same as above. Sufficient.

Answer: D.

Hope it's clear.

Hi Bunuel , if i am not mistaken , why are we assuming that r and s belongs to an evenly spaced set of integers ??

Not sure I understand what you mean.

s and r are just two integers. The question asks: how many integers are there between, but not including r and s.

Ask yourself, how many integers are there between, but not including, 0 and 10? The answer is 9: 1, 2, 3, 4, 5, 6, 7, 8, and 9.
avatar
sharmila79
Joined: 15 May 2012
Last visit: 16 Jun 2014
Posts: 19
Own Kudos:
Given Kudos: 94
Posts: 19
Kudos: 6
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
How many integers are there between, but not including, integers r and s ?

Notice that we are told that r and s are integers.

(1) s – r = 10 --> since r and s are integers and s – r = 10 then there will be 9 integers between them. For example take s=10 and r=0, then there are following integers between them: 1, 2, 3, 4, 5, 6, 7, 8, and 9. Sufficient.

(2) There are 9 integers between, but not including, r + 1 and s + 1 --> the distance between r and s is the same as the distance between r+1 and s+1, so if there are 9 integers between, but not including, r+1 and s+1 then there will be 9 integers between, but not including, r and s too. For example consider s+1=11 and r+1=1 (9 integers between them: 2, 3, 4, 5, 6, 7, 8, 9, and 10) --> s=10 and r=0 the same as above. Sufficient.

Answer: D.

Hope it's clear.
But, Bunuel - Considering your example in the first case in which r=0 and s=10, the number of integers between them could be maximum 9 or it could be any number less than that. Because, there is no mention of the word "consecutive" in the question. But, the second one clearly states that there are 9 integers. Hence B is sufficient, but A is not! Can you please explain where I am going wrong? Since this is an official problem and also you had solved it, I am 100% confident that D is the answer, but, I want to know where I am going wrong.
Thanks!
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,390
Own Kudos:
778,308
 [1]
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,390
Kudos: 778,308
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
sharmila79
Bunuel
How many integers are there between, but not including, integers r and s ?

Notice that we are told that r and s are integers.

(1) s – r = 10 --> since r and s are integers and s – r = 10 then there will be 9 integers between them. For example take s=10 and r=0, then there are following integers between them: 1, 2, 3, 4, 5, 6, 7, 8, and 9. Sufficient.

(2) There are 9 integers between, but not including, r + 1 and s + 1 --> the distance between r and s is the same as the distance between r+1 and s+1, so if there are 9 integers between, but not including, r+1 and s+1 then there will be 9 integers between, but not including, r and s too. For example consider s+1=11 and r+1=1 (9 integers between them: 2, 3, 4, 5, 6, 7, 8, 9, and 10) --> s=10 and r=0 the same as above. Sufficient.

Answer: D.

Hope it's clear.
But, Bunuel - Considering your example in the first case in which r=0 and s=10, the number of integers between them could be maximum 9 or it could be any number less than that. Because, there is no mention of the word "consecutive" in the question. But, the second one clearly states that there are 9 integers. Hence B is sufficient, but A is not! Can you please explain where I am going wrong? Since this is an official problem and also you had solved it, I am 100% confident that D is the answer, but, I want to know where I am going wrong.
Thanks!

You don't need the word "consecutive".

How many integers are there between, but not including 1 and 3? Only one integer: 2.
How many integers are there between, but not including 1 and 5? Three: 2, 3, and 4.

Similarly: how many integers are there between, but not including, 0 and 10? The answer is 9: 1, 2, 3, 4, 5, 6, 7, 8, and 9.

Hope it's clear.
User avatar
Ralphcuisak
Joined: 07 Mar 2013
Last visit: 04 Jun 2016
Posts: 270
Own Kudos:
Given Kudos: 444
Status:The Final Countdown
Concentration: Technology, General Management
GMAT 1: 710 Q47 V41
GPA: 3.84
WE:Information Technology (Computer Software)
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel , why can't s and r be negative?s could be -10 and r could be 20 so s-r would still be 10 but the number of integers would be 30?I'm sure i'm missing something stupid here.
:/
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,390
Own Kudos:
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,390
Kudos: 778,308
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Ralphcuisak
Bunuel , why can't s and r be negative?s could be -10 and r could be 20 so s-r would still be 10 but the number of integers would be 30?I'm sure i'm missing something stupid here.
:/

If s = -10 and r = 20, then s - r = -10 - 20 = -30, not 10.
User avatar
Ralphcuisak
Joined: 07 Mar 2013
Last visit: 04 Jun 2016
Posts: 270
Own Kudos:
Given Kudos: 444
Status:The Final Countdown
Concentration: Technology, General Management
GMAT 1: 710 Q47 V41
GPA: 3.84
WE:Information Technology (Computer Software)
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Oh.i knew its something stupid.This warrants a break.Thanks a ton Bunuel . You rock.
:|
User avatar
ash99
Joined: 12 Apr 2013
Last visit: 03 Feb 2017
Posts: 18
Own Kudos:
128
 [1]
Given Kudos: 20
Concentration: Entrepreneurship, Strategy
Products:
Posts: 18
Kudos: 128
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
The number of integers between two numbers r and s (including both numbers) is s - r +1
The number of integers between two numbers r and s (excluding both numbers) is s - r - 1

Basically the question is asking the value of (s - r - 1)?

(1) s - r = 10.
10 - 1 = 9 Sufficient

(2) There are 9 integers between, but not including, r + 1 and s + 1.

[(s + 1) - (r + 1) - 1] = 9
or (s - r - 1 ) = 9 Sufficient

Hence D.
User avatar
Kchaudhary
Joined: 04 Dec 2016
Last visit: 10 Sep 2018
Posts: 58
Own Kudos:
Given Kudos: 52
Posts: 58
Kudos: 68
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel
SOLUTION

How many integers are there between, but not including, integers r and s ?

Notice that we are told that r and s are integers.

(1) s – r = 10 --> since r and s are integers and s – r = 10 then there will be 9 integers between them. For example take s=10 and r=0, then there are following integers between them: 1, 2, 3, 4, 5, 6, 7, 8, and 9. Sufficient.

(2) There are 9 integers between, but not including, r + 1 and s + 1 --> the distance between r and s is the same as the distance between r+1 and s+1, so if there are 9 integers between, but not including, r+1 and s+1 then there will be 9 integers between, but not including, r and s too. For example consider s+1=11 and r+1=1 (9 integers between them: 2, 3, 4, 5, 6, 7, 8, 9, and 10) --> s=10 and r=0 the same as above. Sufficient.

Answer: D.

Hi Bunuel, how to know that the integers between r and s are consecutive integers?
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,390
Own Kudos:
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,390
Kudos: 778,308
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Kchaudhary
Bunuel
SOLUTION

How many integers are there between, but not including, integers r and s ?

Notice that we are told that r and s are integers.

(1) s – r = 10 --> since r and s are integers and s – r = 10 then there will be 9 integers between them. For example take s=10 and r=0, then there are following integers between them: 1, 2, 3, 4, 5, 6, 7, 8, and 9. Sufficient.

(2) There are 9 integers between, but not including, r + 1 and s + 1 --> the distance between r and s is the same as the distance between r+1 and s+1, so if there are 9 integers between, but not including, r+1 and s+1 then there will be 9 integers between, but not including, r and s too. For example consider s+1=11 and r+1=1 (9 integers between them: 2, 3, 4, 5, 6, 7, 8, 9, and 10) --> s=10 and r=0 the same as above. Sufficient.

Answer: D.

Hi Bunuel, how to know that the integers between r and s are consecutive integers?

Integers between r and s consists of all the integers between r and s, so they ARE consecutive. For example, integers between 5 and 10 are 6, 7, 8, and 9, which are naturally consecutive.
User avatar
longhaul123
Joined: 03 Jul 2017
Last visit: 11 Nov 2018
Posts: 139
Own Kudos:
Given Kudos: 27
Status:IF YOU CAN DREAM IT, YOU CAN DO IT
Location: India
Concentration: Finance, International Business
Posts: 139
Kudos: 35
Kudos
Add Kudos
Bookmarks
Bookmark this Post
one small doubt in the statement 1. Why shouldn't we consider s=-10 and r=20 in which case the sum is 10 but the number of integers between them is not 9. Kindly explain
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 19 Nov 2025
Posts: 105,390
Own Kudos:
Given Kudos: 99,977
Products:
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,390
Kudos: 778,308
Kudos
Add Kudos
Bookmarks
Bookmark this Post
longhaul123
one small doubt in the statement 1. Why shouldn't we consider s=-10 and r=20 in which case the sum is 10 but the number of integers between them is not 9. Kindly explain

(1) says that s – r = 10.

If s = -10 and r = 20, then s - r = -10 - 20 = -30, not 10.
 1   2   
Moderators:
Math Expert
105390 posts
496 posts