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Math Revolution GMAT Instructor
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If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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03 Aug 2017, 01:26
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If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2digit integer ab is divisible by 3. 2) When c is divided by 3, the remainder is 0.
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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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03 Aug 2017, 02:44
Statement 1: let a=3 and b=2 then ab=6 which is divisble by 3 then putting the value in the eq we get 5c which is not divisible by 3 so no put a=3 and b=3 then ab is divisible by 3 and also 6c which is divisible by 3 so yes Insufficient Statement 2: since c is divisible by 3 therefore (a+b)c is also divisible by 3 Sufficient Ans: B Sent from my SMJ210F using GMAT Club Forum mobile app



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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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03 Aug 2017, 09:09
Is "two digit integer ab" supposed to reflect a number where a is the tens digit, and b the ones digit? Or does it mean the product of a and b?



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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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03 Aug 2017, 10:49
Statement 1: ab = 10a+b = (a+b)+9a is divisible by 3 so a+b is divisible by 3 Statement 2: Obvious yes



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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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06 Aug 2017, 18:13
==> If you modify the original condition and the question, in order to have (a+b)c to be divided by 3, a+b or c has to be divided by 3. However, if you look at con 2), c is divisible by 3, hence it is yes and sufficient. For con 1), ab is also divisible by 3, and thus a+b is also divisible by 3, hence it is yes and sufficient. Therefore, the answer is D. This type of question is a 5051level question which applies CMT 4 (B: if you get A or B too easily, consider D). Answer: D
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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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07 May 2019, 22:41
MathRevolution wrote: ==> If you modify the original condition and the question, in order to have (a+b)c to be divided by 3, a+b or c has to be divided by 3. However, if you look at con 2), c is divisible by 3, hence it is yes and sufficient. For con 1), ab is also divisible by 3, and thus a+b is also divisible by 3, hence it is yes and sufficient. Therefore, the answer is D. This type of question is a 5051level question which applies CMT 4 (B: if you get A or B too easily, consider D).
Answer: D I am not following your logic for con 1). If a=1 and b=3, then ab=3 divisible by 3, however a+b=4 so it would not be true. I am still not convinced that B is the right answer. Could you please elaborate ?



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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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15 May 2019, 11:30
krasha wrote: MathRevolution wrote: ==> If you modify the original condition and the question, in order to have (a+b)c to be divided by 3, a+b or c has to be divided by 3. However, if you look at con 2), c is divisible by 3, hence it is yes and sufficient. For con 1), ab is also divisible by 3, and thus a+b is also divisible by 3, hence it is yes and sufficient. Therefore, the answer is D. This type of question is a 5051level question which applies CMT 4 (B: if you get A or B too easily, consider D).
Answer: D I am not following your logic for con 1). If a=1 and b=3, then ab=3 divisible by 3, however a+b=4 so it would not be true. I am still not convinced that B is the right answer. Could you please elaborate ? I had the same confusion! I agree with your approach



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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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15 May 2019, 17:08
MathRevolution wrote: If a, b, and c are positive integers, is (a+b)c divisible by 3?
1) 2digit integer ab is divisible by 3. 2) When c is divided by 3, the remainder is 0. Let's start with statement 2, c= 3K, so (a+b)c is definitely divisible by 3. Now, statement 1, TU ab 21 48 All two digit numbers (Any numbers) that are divisible by three their sum is also divisible by 3. This is divisibility rule of three. So, (a+b) must be divisible by three. Either statement independently sufficient.
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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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15 May 2019, 22:49
LeoN88 wrote: MathRevolution wrote: If a, b, and c are positive integers, is (a+b)c divisible by 3?
1) 2digit integer ab is divisible by 3. 2) When c is divided by 3, the remainder is 0. Let's start with statement 2, c= 3K, so (a+b)c is definitely divisible by 3. Now, statement 1, TU ab 21 48 All two digit numbers (Any numbers) that are divisible by three their sum is also divisible by 3. This is divisibility rule of three. So, (a+b) must be divisible by three. Either statement independently sufficient. I think I know where the confusion comes from. ab doesn’t have a multiplication sign between them. It is not a.b, it is ab without the multiplication. However, I still think the positioning of the question is a bit confusing Posted from my mobile device



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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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16 May 2019, 08:23
Sorry, I also don’t get, how ab divisible by 3 get us a+b divisible by 3 3*4 div by 3, but 3+4 is not... Pls explain and give us several examples.
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Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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16 May 2019, 08:26
nyashka wrote: Sorry, I also don’t get, how ab divisible by 3 get us a+b divisible by 3 3*4 div by 3, but 3+4 is not... Pls explain and give us several examples.
Posted from my mobile device Oh, sorry, I got it... E.g. 12 is a twodigit number, it is divisible by 3, and the sum of the DIGITS is also divisible Hence the answer is really D.




Re: If a, b, and c are positive integers, is (a+b)c divisible by 3? 1) 2
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16 May 2019, 08:26






