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What is the value of ab? (1) a + b = a (2) a + b = b
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30 Apr 2013, 04:26
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54% (01:55) correct 46% (01:50) wrong based on 298 sessions
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What is the value of ab? (1) a + b = a (2) a + b = b I cant combine the two statements and reach anywhere  1. a + b = a we wil have two cases once a positive and once a negative  when a positive a+b = a implies b =0 when a ve a+b=a b=2a
so by statement  either ab = 0 (when b is zero) or ab= 2a² (when b=2a) (we dont know the value of a)
so we dont have one unique value of b
Statement II a + b = b either a = 0 or a= 2b again we dont get a clear value for ab.
can someone please tell me if my approach so far is ok and how do I combine the two statements now....thanks.
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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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30 Apr 2013, 04:36




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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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30 Apr 2013, 04:38



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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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30 Apr 2013, 09:55
Bunuel wrote: What is the value of ab?
(1) a + b = a. Just plug numbers to see that this statement is NOT sufficient: if a=b=0, then ab=0 but if a=1 and b=2, then ab=2. Not sufficient.
(2) a + b = b. The same here. Not sufficient.
(1)+(2) Sum (1) and (2): a + b + a + b= a + b > a + b = 0. The sum of two nonnegative values (a and b) to be 0, each must be 0, thus a=b=0 > ab=0. Sufficient.
Answer: C.
Hope it's clear. Bunuel  Thanks for the reply. I understood the way you did that. Could you please go through my explanation once please and see if that is also fine or have I done soemthing wrong? also is there a way to combine the two statements without literally adding them...I mean the way I solved it..I reached at b=0 and 2a from Ist statement and a=0, and 2b from IInd statement....is there a way I can combine them from this point? I am usually we look for a common point from the outcomes of two statements when we combine them, can we do that here. Thanks. Kind regards..



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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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02 May 2013, 02:55
tirbah wrote: Bunuel wrote: What is the value of ab?
(1) a + b = a. Just plug numbers to see that this statement is NOT sufficient: if a=b=0, then ab=0 but if a=1 and b=2, then ab=2. Not sufficient.
(2) a + b = b. The same here. Not sufficient.
(1)+(2) Sum (1) and (2): a + b + a + b= a + b > a + b = 0. The sum of two nonnegative values (a and b) to be 0, each must be 0, thus a=b=0 > ab=0. Sufficient.
Answer: C.
Hope it's clear. Bunuel  Thanks for the reply. I understood the way you did that. Could you please go through my explanation once please and see if that is also fine or have I done soemthing wrong? also is there a way to combine the two statements without literally adding them...I mean the way I solved it..I reached at b=0 and 2a from Ist statement and a=0, and 2b from IInd statement....is there a way I can combine them from this point? I am usually we look for a common point from the outcomes of two statements when we combine them, can we do that here. Thanks. Kind regards.. Your reasoning for (1) and (2) is correct: (1) a + b = a. a<0 > b=2a a>=0 > b=0 (2) a + b = b b<0 > a=2b (b=a/2) b>=0 > a=0 (1)+(2) If a<0, then from b=2a, b<0 too. Thus we have that when a<0 and b<0, then b=2a and b=a/2, which cannot be true. So,we are left with a=b=0. Hope it's clear.
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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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02 May 2013, 05:11
Bunuel wrote: tirbah wrote: Bunuel wrote: What is the value of ab?
(1) a + b = a. Just plug numbers to see that this statement is NOT sufficient: if a=b=0, then ab=0 but if a=1 and b=2, then ab=2. Not sufficient.
(2) a + b = b. The same here. Not sufficient.
(1)+(2) Sum (1) and (2): a + b + a + b= a + b > a + b = 0. The sum of two nonnegative values (a and b) to be 0, each must be 0, thus a=b=0 > ab=0. Sufficient.
Answer: C.
Hope it's clear. Bunuel  Thanks for the reply. I understood the way you did that. Could you please go through my explanation once please and see if that is also fine or have I done soemthing wrong? also is there a way to combine the two statements without literally adding them...I mean the way I solved it..I reached at b=0 and 2a from Ist statement and a=0, and 2b from IInd statement....is there a way I can combine them from this point? I am usually we look for a common point from the outcomes of two statements when we combine them, can we do that here. Thanks. Kind regards.. Your reasoning for (1) and (2) is correct: (1) a + b = a. a<0 > b=2a a>=0 > b=0 (2) a + b = b b<0 > a=2b (b=a/2) b>=0 > a=0 (1)+(2) If a<0, then from b=2a, b<0 too. Thus we have that when a<0 and b<0, then b=2a and b=a/2, which cannot be true. So,we are left with a=b=0. Hope it's clear. Yes I understood it now...Thank you so much.



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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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18 Aug 2014, 02:04
Q What is the value of ab? 1. a + b = a 2. a + b = b STAT1 Take two cases Case 1: a is >=0 a = a => b = 0 so, ab=0 Case 2: a< 0 => a = a a + b = a => b = 2a ab = 2a^2 Both are different so not sufficient STAT2 Take two cases Case 1: b>= 0 b = b so, a+ b = b => a = 0 => ab = 0 Case 2: b<0 => b = b => a  b = b => a = 2b => ab = 2b^2 Both are different so NoT sufficient Takeing STAT1 and STAT2 together there will be 4 cases adding both the equations we get a + b +a +b = a+ b => a +b = 0 Only possible when both a=b=0 => ab=0 So, asnwer will be C Hope it helps!
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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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18 Aug 2014, 02:21



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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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30 Nov 2015, 09:45
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution. What is the value of ab? 1. a + b = a 2. a + b = b There are 2 variables (a,b) and 2 equations are given by the 2 conditions, so there is high chance (C) will be the answer. Looking at the conditions together, a=b=0 > ab=0. This is unique and sufficient, the answer becomes (C). For cases where we need 2 more equations, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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11 Oct 2016, 06:32
Amit0507 wrote: What is the value of ab?
1. a + b = a 2. a + b = b 1. 2 options: a+b=a > b=0, and ab=0 ba=a > b=2a  not sufficient. 2. 2 options: a+b=b > a=0, and ab=0 ab=b > a=2b  not sufficient 1+2 a=0, b=0, b=2a  true, a=2b  true answer is C.



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Re: What is the value of ab? (1) a + b = a (2) a + b = b
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