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fireinbelly
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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 30 Apr 2013, 05:26
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C
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54% (01:55) correct 46% (01:56) wrong based on 386 sessions

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What is the value of ab?

(1) |a| + b = a
(2) a + |b| = b

Show Spoiler
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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C
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Bunuel
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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 30 Apr 2013, 05:36
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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 non-negative values (|a| and |b|) to be 0, each must be 0, thus a=b=0 --> ab=0. Sufficient.

Answer: C.

Hope it's clear.
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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 30 Apr 2013, 05:38
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tirbah
What is the value of ab?

(1) |a| + b = a
(2) a + |b| = b

Show Spoiler
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.
Show more

Similar question to practice: is-xy-132217.html

Hope it helps.
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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 30 Apr 2013, 10:55
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Bunuel
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 non-negative values (|a| and |b|) to be 0, each must be 0, thus a=b=0 --> ab=0. Sufficient.

Answer: C.

Hope it's clear.
Show more

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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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 02 May 2013, 03:55
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tirbah
Bunuel
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 non-negative 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..
Show more

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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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 02 May 2013, 06:11
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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 non-negative 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.
Show more

Yes I understood it now...Thank you so much.
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What is the value of ab? (1) |a| + b = a (2) a + |b| = b Updated on: 30 Oct 2021, 11:32
Originally posted by BrushMyQuant on 18 Aug 2014, 03:04.
Last edited by BrushMyQuant on 30 Oct 2021, 11:32, edited 2 times in total.
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Check out these posts to understand Absolute Value in Detail

How to Solve: Absolute Value (Basics)
How to Solve: Absolute Value Problems

Q What is the value of ab?

1. |a| + b = a
2. a + |b| = b

STAT1
Take two cases
Case 1: a >=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

Taking 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, Answer will be C
Hope it helps!

Watch the following video to learn the Basics of Absolute Values

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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 18 Aug 2014, 03:21
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What is the value of ab?

(1) |a| + b = a --> a - |a| = b --> if a = 1 and b = 0, then ab = 0 but if a = -1 and b = -2, then ab = 2. Not sufficient.

(2) a + |b| = b --> b - |b| = a --> if b = 1 and a = 0, then ab = 0 but if b = -1 and a = -2, then ab = 2. Not sufficient.

(1)+(2) Sum (1) and (2): |a| + b + a + |b| = a + b --> |a| + |b| = 0. The sum of two nonnegative values can be 0, if and only both of them are 0 --> |a| = |b| = 0 --> ab = 0. Sufficient.

Answer: C.

Hope it's clear.
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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 30 Nov 2015, 10:45
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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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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 11 Oct 2016, 07:32
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Amit0507
What is the value of ab?

1. |a| + b = a
2. a + |b| = b
Show more

1. 2 options:
a+b=a -> b=0, and ab=0
b-a=a -> b=2a - not sufficient.

2. 2 options:
a+b=b -> a=0, and ab=0
a-b=b -> a=2b - not sufficient

1+2
a=0, b=0, b=2a - true, a=2b - true
answer is C.
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What is the value of ab? (1) |a| + b = a (2) a + |b| = b 16 May 2021, 03:13
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