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If r and s are integers, is r+s divisible by 3? 1. s is [#permalink]
 23 Dec 2005, 11:06
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If r and s are integers, is r+s divisible by 3?
1. s is divisible by 3
2. r is divisible by 3
Kindly explain your answer. I have a specific doubt in my mind regarding the official explanation for this question. I will post my doubt tomorrow in order to give some time to those interested in taking a stab at this.
Last edited by 5elements on 23 Dec 2005, 13:52, edited 1 time in total.
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Re: DS - is r+s divisible by 3? [#permalink]
23 Dec 2005, 11:56
5elements wrote: If r and s are integers, is r+s divisible by 3?
1. s is divisible by 3
2. r is divisible by 3
Kindly explain your answer. I have a specific doubt in my mind regarding the official explanation for this question. I will post my doubt tomorrow in order some time to give those interested in taking a stab that this.
C.
1) We don't know anything about s.... if r=3, s=6, then yes......if r=3, s=2, then no....INSUFF
2)Same reasoning as 1)....INSUFF
1) and 2) together.... we know that both are multiples of 3, therefore their sum must be divisible by 3.... SUFF
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Re: DS - is r+s divisible by 3? [#permalink]
23 Dec 2005, 12:55
5elements wrote: If r and s are integers, is r+s divisible by 3?
1. s is divisible by 3
2. r is divisible by 3
Kindly explain your answer. I have a specific doubt in my mind regarding the official explanation for this question. I will post my doubt tomorrow in order some time to give those interested in taking a stab that this.
If r and s are integers, is r+s divisible by 3? So its asking if r/3 + s/3 an integer?
It is C.
(1) Tells us nothing about r. Insufficient.
(2) Tells us nothing about s. Insufficient.
(1) + (2) Sufficient
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OA is C. BTW, this OG - DS question 45.
It cannot be A or B, for the reasons stated in the earlier responses by other members.
Now, regarding "C" ... here is my question/doubt
Consider r = -3 and s = 3 . Note, the question stem says that r and s are integers, so it is fair have positive value for one and negative for the other
In this case, r+s = (-3) +(3) = 0.
My understanding is "0" cannot be divided into 3, hence indivisble by 3. If this is true, then the answer should be "E"... what am I missing here?
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5elements wrote: OA is C. BTW, this OG - DS question 45.
It cannot be A or B, for the reasons stated in the earlier responses by other members.
Now, regarding "C" ... here is my question/doubt
Consider r = -3 and s = 3 . Note, the question stem says that r and s are integers, so it is fair have positive value for one and negative for the other
In this case, r+s = (-3) +(3) = 0.
My understanding is "0" cannot be divided into 3, hence indivisble by 3. If this is true, then the answer should be "E"... what am I missing here?
0 is divisible by all numbers.
However any number divided by 0 is undefined
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Clear cut answer C..
As we need both the statements to determine if the sum r+s is divisible by 3
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5elements wrote: OA is C. BTW, this OG - DS question 45.
It cannot be A or B, for the reasons stated in the earlier responses by other members.
Now, regarding "C" ... here is my question/doubt
Consider r = -3 and s = 3 . Note, the question stem says that r and s are integers, so it is fair have positive value for one and negative for the other
In this case, r+s = (-3) +(3) = 0.
My understanding is "0" cannot be divided into 3, hence indivisble by 3. If this is true, then the answer should be "E"... what am I missing here?
We can say X is divisible by Y, when the Remainder is ZERO.
When zero is divided by any number, the remainder is zero......Hence Zero is divisible by all numbers
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Re: DS - is r+s divisible by 3? [#permalink]
25 Dec 2005, 23:48
5elements wrote: If r and s are integers, is r+s divisible by 3?
1. s is divisible by 3
2. r is divisible by 3
Kindly explain your answer. I have a specific doubt in my mind regarding the official explanation for this question. I will post my doubt tomorrow in order to give some time to those interested in taking a stab at this.
From 1, we get s = 0 mod 3. Nothing is known about r. so insuff.
From 2 we get r = 0 mod 3, nothing is known about s. So insuff.
Addding 1 +2 we get r+s = 0 mod 3. Hence C.
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Re: DS - is r+s divisible by 3?
[#permalink]
25 Dec 2005, 23:48
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