It is currently 18 Mar 2018, 10:42

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

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

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If r – s = 3p , is p an integer? (1) r is divisible by 735

Author Message
TAGS:

Hide Tags

Director
Status: Finally Done. Admitted in Kellogg for 2015 intake
Joined: 25 Jun 2011
Posts: 521
Location: United Kingdom
GMAT 1: 730 Q49 V45
GPA: 2.9
WE: Information Technology (Consulting)
If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

21 Jan 2012, 15:46
1
KUDOS
24
This post was
BOOKMARKED
00:00

Difficulty:

35% (medium)

Question Stats:

67% (01:07) correct 33% (01:03) wrong based on 421 sessions

HideShow timer Statistics

If r – s = 3p , is p an integer?

(1) r is divisible by 735
(2) r + s is divisible by 3

[Reveal] Spoiler:
OA is C. I am struggling to find how. This is how I approaching the question. Can someone please help?

Considering Questions Stem

We have to find whether r-s/3 as p is an integer?

Considering statement 1

r is a factor of 735. That means r is divisible by all factors of 735 and 3 is a factor of 735 [Because 7+3+5=15]. But as the statement doesn't mention anything about s, it's INSUFFICIENT to answer the question.

Considering statement 2

r+s is divisible by 3

Case 1

r=6 s = 3 then r+s and r-s both divisible by 3.

Case 2
r=7 and s =5 then r+s is divisible by 3 and r-s is NOT divisible by 3. Therefore this statement alone is INSUFFICIENT.

Now combining the two statements : I am struggling after this?
[Reveal] Spoiler: OA

_________________

Best Regards,
E.

MGMAT 1 --> 530
MGMAT 2--> 640
MGMAT 3 ---> 610
GMAT ==> 730

Last edited by HKD1710 on 07 Oct 2017, 06:56, edited 1 time in total.
Math Expert
Joined: 02 Sep 2009
Posts: 44295
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

21 Jan 2012, 16:01
8
KUDOS
Expert's post
17
This post was
BOOKMARKED
enigma123 wrote:
If r – s = 3p, is p an integer?
(1) r is divisible by 735
(2) r + s is divisible by 3

If r – s = 3p , is p an integer?

Question basically asks whether r-s is a multiple of 3 (..., -6, -3, 0, 3, 6, ...), because if it is then p would be an integer.

(1) r is divisible by 735 --> r is a multiple of 3 (as the sum of the digits of 735 is divisible by 3), though this statement is insufficient as no info about s.

(2) r + s is divisible by 3 --> r + s is a multiple of 3. Now, if r=2 and s=1 then r-s=1 and the answer is NO but if r=s=0 then r-s=0 and the answer is YES. Not sufficient.

(1)+(2) From (1) r={multiple of 3} then as from (2) r+s={multiple of 3}+s={multiple of 3} then s is also a multiple of 3 --> r-s={multiple of 3}-{multiple of 3}={multiple of 3}. Sufficient.

Below might help to understand this concept better.

If integers $$a$$ and $$b$$ are both multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference will also be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$ and $$b=9$$, both divisible by 3 ---> $$a+b=15$$ and $$a-b=-3$$, again both divisible by 3.

If out of integers $$a$$ and $$b$$ one is a multiple of some integer $$k>1$$ and another is not, then their sum and difference will NOT be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$, divisible by 3 and $$b=5$$, not divisible by 3 ---> $$a+b=11$$ and $$a-b=1$$, neither is divisible by 3.

If integers $$a$$ and $$b$$ both are NOT multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference may or may not be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=5$$ and $$b=4$$, neither is divisible by 3 ---> $$a+b=9$$, is divisible by 3 and $$a-b=1$$, is not divisible by 3;
OR: $$a=6$$ and $$b=3$$, neither is divisible by 5 ---> $$a+b=9$$ and $$a-b=3$$, neither is divisible by 5;
OR: $$a=2$$ and $$b=2$$, neither is divisible by 4 ---> $$a+b=4$$ and $$a-b=0$$, both are divisible by 4.

Hope it's clear.
_________________
Director
Status: Finally Done. Admitted in Kellogg for 2015 intake
Joined: 25 Jun 2011
Posts: 521
Location: United Kingdom
GMAT 1: 730 Q49 V45
GPA: 2.9
WE: Information Technology (Consulting)
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

21 Jan 2012, 16:15
1
KUDOS
Classic explanation. Thanks very much.
_________________

Best Regards,
E.

MGMAT 1 --> 530
MGMAT 2--> 640
MGMAT 3 ---> 610
GMAT ==> 730

Intern
Joined: 27 Nov 2011
Posts: 7
Location: India
Concentration: Technology, Marketing
GMAT 1: 660 Q47 V34
GMAT 2: 710 Q47 V41
WE: Consulting (Consulting)
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

25 May 2012, 01:18
Bunuel wrote:
enigma123 wrote:
If r – s = 3p, is p an integer?
(1) r is divisible by 735
(2) r + s is divisible by 3

If r – s = 3p , is p an integer?

Question basically asks whether r-s is a multiple of 3 (..., -6, -3, 0, 3, 6, ...), because if it is then p would be an integer.

(1) r is divisible by 735 --> r is a multiple of 3 (as the sum of the digits of 735 is divisible by 3), though this statement is insufficient as no info about s.

(2) r + s is divisible by 3 --> r + s is a multiple of 3. Now, if r=2 and s=1 then r-s=1 and the answer is NO but if r=s=0 then r-s=0 and the answer is YES. Not sufficient.

(1)+(2) From (1) r={multiple of 3} then as from (2) r+s={multiple of 3}+s={multiple of 3} then s is also a multiple of 3 --> r-s={multiple of 3}-{multiple of 3}={multiple of 3}. Sufficient.

Below might help to understand this concept better.

If integers $$a$$ and $$b$$ are both multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference will also be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$ and $$b=9$$, both divisible by 3 ---> $$a+b=15$$ and $$a-b=-3$$, again both divisible by 3.

If out of integers $$a$$ and $$b$$ one is a multiple of some integer $$k>1$$ and another is not, then their sum and difference will NOT be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$, divisible by 3 and $$b=5$$, not divisible by 3 ---> $$a+b=11$$ and $$a-b=1$$, neither is divisible by 3.

If integers $$a$$ and $$b$$ both are NOT multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference may or may not be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=5$$ and $$b=4$$, neither is divisible by 3 ---> $$a+b=9$$, is divisible by 3 and $$a-b=1$$, is not divisible by 3;
OR: $$a=6$$ and $$b=3$$, neither is divisible by 5 ---> $$a+b=9$$ and $$a-b=3$$, neither is divisible by 5;
OR: $$a=2$$ and $$b=2$$, neither is divisible by 4 ---> $$a+b=4$$ and $$a-b=0$$, both are divisible by 4.

Hope it's clear.

Hi,

I think B should be sufficient. Here is how:

We are given r+s is divisible by 3.

r+s=3a (where a is any integer) -----(1)
r-s+2s = 3a
3p + 2s = 3a (since we are given that r-s=3p)
2s = 3(a-p)
since 2 and 3 are both primes, we can conclude that a-p is a multiple of 2 and s is a multiple of 3.

similarly if we replace r by (-r+2r), we will get that r is also divisible by 3.

hence, if both r and s are divisible by 3, therefore p is an integer.

please correct me if i am wrong somewhere.

Math Expert
Joined: 02 Sep 2009
Posts: 44295
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

25 May 2012, 01:32
Expert's post
1
This post was
BOOKMARKED
kunalbh19 wrote:
Bunuel wrote:
enigma123 wrote:
If r – s = 3p, is p an integer?
(1) r is divisible by 735
(2) r + s is divisible by 3

If r – s = 3p , is p an integer?

Question basically asks whether r-s is a multiple of 3 (..., -6, -3, 0, 3, 6, ...), because if it is then p would be an integer.

(1) r is divisible by 735 --> r is a multiple of 3 (as the sum of the digits of 735 is divisible by 3), though this statement is insufficient as no info about s.

(2) r + s is divisible by 3 --> r + s is a multiple of 3. Now, if r=2 and s=1 then r-s=1 and the answer is NO but if r=s=0 then r-s=0 and the answer is YES. Not sufficient.

(1)+(2) From (1) r={multiple of 3} then as from (2) r+s={multiple of 3}+s={multiple of 3} then s is also a multiple of 3 --> r-s={multiple of 3}-{multiple of 3}={multiple of 3}. Sufficient.

Below might help to understand this concept better.

If integers $$a$$ and $$b$$ are both multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference will also be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$ and $$b=9$$, both divisible by 3 ---> $$a+b=15$$ and $$a-b=-3$$, again both divisible by 3.

If out of integers $$a$$ and $$b$$ one is a multiple of some integer $$k>1$$ and another is not, then their sum and difference will NOT be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$, divisible by 3 and $$b=5$$, not divisible by 3 ---> $$a+b=11$$ and $$a-b=1$$, neither is divisible by 3.

If integers $$a$$ and $$b$$ both are NOT multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference may or may not be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=5$$ and $$b=4$$, neither is divisible by 3 ---> $$a+b=9$$, is divisible by 3 and $$a-b=1$$, is not divisible by 3;
OR: $$a=6$$ and $$b=3$$, neither is divisible by 5 ---> $$a+b=9$$ and $$a-b=3$$, neither is divisible by 5;
OR: $$a=2$$ and $$b=2$$, neither is divisible by 4 ---> $$a+b=4$$ and $$a-b=0$$, both are divisible by 4.

Hope it's clear.

Hi,

I think B should be sufficient. Here is how:

We are given r+s is divisible by 3.

r+s=3a (where a is any integer) -----(1)
r-s+2s = 3a
3p + 2s = 3a (since we are given that r-s=3p)
2s = 3(a-p)
since 2 and 3 are both primes, we can conclude that a-p is a multiple of 2 and s is a multiple of 3.

similarly if we replace r by (-r+2r), we will get that r is also divisible by 3.

hence, if both r and s are divisible by 3, therefore p is an integer.

please correct me if i am wrong somewhere.

OA for this question is C, not B. OA is given in the initial post under the spoiler.

Next, for the second statement there are two examples given in my post which give different answer to the question whether p is an integer.

(2) r + s is divisible by 3 --> r + s is a multiple of 3. Now, if r=2 and s=1 then r-s=1 and the answer is NO but if r=s=0 then r-s=0 and the answer is YES. Not sufficient.
_________________
Intern
Joined: 29 Aug 2012
Posts: 26
Schools: Babson '14
GMAT Date: 02-28-2013
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

06 Nov 2012, 05:23
1
KUDOS
The above mentioned solution is valid for integers .... What if s is a fraction say 3/4 ... The answer should be E in that case..
Math Expert
Joined: 02 Sep 2009
Posts: 44295
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

06 Nov 2012, 05:32
3
KUDOS
Expert's post
himanshuhpr wrote:
The above mentioned solution is valid for integers .... What if s is a fraction say 3/4 ... The answer should be E in that case..

(1) says that r is divisible by 735, which implies that r is an integer. Next, (2) says that r + s is divisible by 3, which implies that r +s is an integer and since r is an integer then so is s. Thus, when we consider the two statements together we know that both r and s are integers.

On GMAT when we are told that $$a$$ is divisible by $$b$$ (or which is the same: "$$a$$ is multiple of $$b$$", or "$$b$$ is a factor of $$a$$"), we can say that:
1. $$a$$ is an integer;
2. $$b$$ is an integer;
3. $$\frac{a}{b}=integer$$.

So the terms "divisible", "multiple", "factor" ("divisor") are used only about integers (at least on GMAT).

Hope it helps.
_________________
Intern
Joined: 29 Aug 2012
Posts: 26
Schools: Babson '14
GMAT Date: 02-28-2013
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

06 Nov 2012, 05:36
Thank you Bunuel , it's a new and very important thing which I have come to know.
Manager
Joined: 07 May 2012
Posts: 73
Location: United States
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

06 May 2013, 13:32
kunalbh19 wrote:
Bunuel wrote:
enigma123 wrote:
If r – s = 3p, is p an integer?
(1) r is divisible by 735
(2) r + s is divisible by 3

If r – s = 3p , is p an integer?

Question basically asks whether r-s is a multiple of 3 (..., -6, -3, 0, 3, 6, ...), because if it is then p would be an integer.

(1) r is divisible by 735 --> r is a multiple of 3 (as the sum of the digits of 735 is divisible by 3), though this statement is insufficient as no info about s.

(2) r + s is divisible by 3 --> r + s is a multiple of 3. Now, if r=2 and s=1 then r-s=1 and the answer is NO but if r=s=0 then r-s=0 and the answer is YES. Not sufficient.

(1)+(2) From (1) r={multiple of 3} then as from (2) r+s={multiple of 3}+s={multiple of 3} then s is also a multiple of 3 --> r-s={multiple of 3}-{multiple of 3}={multiple of 3}. Sufficient.

Below might help to understand this concept better.

If integers $$a$$ and $$b$$ are both multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference will also be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$ and $$b=9$$, both divisible by 3 ---> $$a+b=15$$ and $$a-b=-3$$, again both divisible by 3.

If out of integers $$a$$ and $$b$$ one is a multiple of some integer $$k>1$$ and another is not, then their sum and difference will NOT be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=6$$, divisible by 3 and $$b=5$$, not divisible by 3 ---> $$a+b=11$$ and $$a-b=1$$, neither is divisible by 3.

If integers $$a$$ and $$b$$ both are NOT multiples of some integer $$k>1$$ (divisible by $$k$$), then their sum and difference may or may not be a multiple of $$k$$ (divisible by $$k$$):
Example: $$a=5$$ and $$b=4$$, neither is divisible by 3 ---> $$a+b=9$$, is divisible by 3 and $$a-b=1$$, is not divisible by 3;
OR: $$a=6$$ and $$b=3$$, neither is divisible by 5 ---> $$a+b=9$$ and $$a-b=3$$, neither is divisible by 5;
OR: $$a=2$$ and $$b=2$$, neither is divisible by 4 ---> $$a+b=4$$ and $$a-b=0$$, both are divisible by 4.

Hope it's clear.

Hi,

I think B should be sufficient. Here is how:

We are given r+s is divisible by 3.

r+s=3a (where a is any integer) -----(1)
r-s+2s = 3a
3p + 2s = 3a (since we are given that r-s=3p)
2s = 3(a-p)
since 2 and 3 are both primes, we can conclude that a-p is a multiple of 2 and s is a multiple of 3.

similarly if we replace r by (-r+2r), we will get that r is also divisible by 3.

hence, if both r and s are divisible by 3, therefore p is an integer.

please correct me if i am wrong somewhere.

I did the same mistake as you and assumed statement 2 by itself would suffice .
After pondering on it for a while , figured where I went wrong.

r+s=3a (where a is any integer) -----(1)
r-s+2s = 3a
3p + 2s = 3a (since we are given that r-s=3p)
2s = 3(a-p)
since 2 and 3 are both primes, we can conclude that a-p is a multiple of 2 and s is a multiple of 3.

Let me try to explain why statement 2 can be insufficient.
2s=3(a-p) . you got it right till here.
But you cannot conclude with just statement 2 , that a-p is a multiple of 2 . Cos all we know untill this point is "a" is an integer. We do not know weather S or/and P is an integer .
To illustrate what I mean above, lemme give you an example -
consider 2s=3(a-p) ===> 2 (0.3) = 3(0.2) , where s=0.3 and a-p=0.2 , a is an integer , lets say 2 , in which case P would be 1.8 . Hence we can prove that p is not an integer.
similarly , we can prove otherwise that P is an integer.

Now if you consider statement 1 , which says S is an integer , we can conclude from the equation 2S=3(a-p) , that P is an integer.
cos 2*integer = 3 * integer , i.e a-p SHOULD be an integer , since a is an integer and S is an integer .

Hope that helps
Jyothi
_________________

Jyothi hosamani

Intern
Joined: 03 Jan 2014
Posts: 2
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

20 Feb 2014, 10:33
Terrific Bunuel, the way you have explained the solution is just amazing. +1 kudos for the excellent concept explained
Intern
Joined: 23 Apr 2014
Posts: 11
Location: India
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

01 Jul 2014, 03:42
Clearly p=(r-s)/3

Statement 1

r is divisible by 735,so p=(735x-s)/3=245x-s/3……..not sufficient

Statement 2

r+s=3y↪↪p=(3y-s-s)/3=(3y-2s)/3=y-2s/3…….not sufficient

Combining (1)+(2)
p=(735x-s)/3

p=(735x-3y-r)/3

now r is a multiple of 3,so it is a multiple of 3

therefore,p=(735x-3y-3z)/3=integer…..sufficient

Intern
Joined: 04 Feb 2016
Posts: 1
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

13 Apr 2017, 01:47
1] r=735k (k is any integer)
We can just say that r is an integer. Nothing known about s.
So not sufficient.

2] r+s=3p
Again, we can just say that r+s is an integer. nothing known independently of r and s.
For example r=7/3, s=2/3, r+s=3 but r-s=5/3
So not sufficient.

Combined, r is an integer and s is also an integer.
Sufficient. Ans C.
Intern
Joined: 07 Jun 2017
Posts: 1
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

07 Jun 2017, 12:57
This question can be rephrased: Is r – s divisible by 3? Or, are r and s each divisible by 3?
Statement (1) tells us that r is divisible by 735. If r is divisible by 735, it is also divisible by all the factors of 735. 3 is a factor of 735. (To test whether 3 is a factor of a number, sum its digits; if the sum is divisible by 3, then 3 is a factor of the number.) However, statement (1) does not tell us anything about whether or not s is divisible by 3. Therefore it is insufficient.
Statement (2) tells us that r + s is divisible by 3. This information alone is insufficient. Consider each of the following two cases:
CASEONE:Ifr=9,ands=6,r+s=15whichisdivisibleby3,and r–s=3,whichisalsodivisibleby3. CASETWO:Ifr=7ands=5,r+s=12,whichisdivisibleby3,but r–s=2,whichisNOTdivisibleby3.
Let's try both statements together. There is a mathematical rule that states that if two integers are each divisible by the integer x, then the sum or difference of those two integers is also divisible by x.
We know from statement (1) that r is divisible by 3. We know from statement (2) that r + s is divisible by 3. Using the converse of the aforementioned rule, we can deduce that s is divisible by 3. Then, using the rule itself, we know that the difference r – s is also divisible by 3.
: BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is
sufficient.
Intern
Joined: 03 Sep 2017
Posts: 2
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

07 Oct 2017, 04:45
I feel B is sufficient.

r-s=3p
If we add 2s on both sides:
r+s=3p+2s
Hence, 3p+2s is divisible by 3.
Since 3p is separately divisible by 3, 2s has to be divisible by 3.
For 2s to be divisible by 3, s has to be divisible by 3.
We already know r+s is divisible by 3. Now we have s is divisible by 3.
Thus r is divisible by 3.(same logic as above)
Hence we get that both s and r are divisible by 3 from statement (ii).

Please do correct me if I'm wrong.

Thanks
Math Expert
Joined: 02 Sep 2009
Posts: 44295
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735 [#permalink]

Show Tags

07 Oct 2017, 04:49
Srisk wrote:
I feel B is sufficient.

r-s=3p
If we add 2s on both sides:
r+s=3p+2s
Hence, 3p+2s is divisible by 3.
Since 3p is separately divisible by 3, 2s has to be divisible by 3.
For 2s to be divisible by 3, s has to be divisible by 3.
We already know r+s is divisible by 3. Now we have s is divisible by 3.
Thus r is divisible by 3.(same logic as above)
Hence we get that both s and r are divisible by 3 from statement (ii).

Please do correct me if I'm wrong.

Thanks

OA for this question is C, not B. OA is given in the initial post under the spoiler.

Next, for the second statement there are two examples given in my post which give different answer to the question whether p is an integer.

(2) r + s is divisible by 3 --> r + s is a multiple of 3. Now, if r=2 and s=1 then r-s=1 and the answer is NO but if r=s=0 then r-s=0 and the answer is YES. Not sufficient.
_________________
Re: If r – s = 3p , is p an integer? (1) r is divisible by 735   [#permalink] 07 Oct 2017, 04:49
Display posts from previous: Sort by