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What is the value of x^3?

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Math Expert
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What is the value of x^3? [#permalink]

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17 Feb 2016, 02:33
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What is the value of x^3?

(1) |x|=2
(2) 5x+6=16

Kudos for correct solution.
[Reveal] Spoiler: OA

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Director
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Re: What is the value of x^3? [#permalink]

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17 Feb 2016, 09:50
3
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Bunuel wrote:
What is the value of x^3?

(1) |x|=2
(2) 5x+6=16

Kudos for correct solution.

(1) IXI=2
x=2,-2
so X^3=8,-8
not sufff..
(2) 5X+6=16

x=2
so X^3=8 suff.
Ans B

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Math Revolution GMAT Instructor
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Re: What is the value of x^3? [#permalink]

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17 Feb 2016, 22:08
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 x^3?

(1) |x|=2
(2) 5x+6=16

In the original condition, there is 1 variable(x), which should match with the number of equations. So you need 1 equation. For 1) 1 equation, for 2) 1 equation, which is likely to make D the answer.
For 1), x^3=-8,8 is derived from x=-2,2, which is not unique and not sufficient.
For 2), 5x=10, x=3, x^3=8 is derived, which is unique and sufficient.

 For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.
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Re: What is the value of x^3? [#permalink]

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17 Feb 2016, 22:38
1
KUDOS
Here the concept tested is one property of even and odd powers
Even powers will result in a +ve sign always
ODD powers will have the same sign of the variable. So for ODD powers it is must to know the sign of variable
S1 : +2 or -2 ( sign not fixed)
S2 = sign and value both are confirmed
So B

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VP
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Re: What is the value of x^3? [#permalink]

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18 Feb 2016, 06:52
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(1) |x|=2..........> X=2, X^3=8 or X=-2, X^3=-8 Ins

(2) 5x+6=16.....> X=2, X^3=8 Suf

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Intern
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Re: What is the value of x^3? [#permalink]

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18 Feb 2016, 15:48
2
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(1) IXI=2
x=2,-2
so X^3=8,-8
not sufff..
(2) 5X+6=16

x=2
so X^3=8 suff.
Ans B . WE KNOW THAT MODS CAN BE POSITIVE OR NEGATIVE , SO WE CANT GET UNIQUE VALUES.
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Please award kudos if you like my explanation.
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Re: What is the value of x^3? [#permalink]

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17 May 2016, 13:52
1
KUDOS
Statement 1 states |x|=2 which means that x can be either +2 or -2 so clearly insufficient as we would get 2 values of $$x^3$$
Statement 2 states 5x+6=16 which can simplified as 5x = 10 which gives x = 2 so we get a definite value of $$x^3$$ which is $$2^3$$ = $$8$$
so sufficient

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Senior Manager
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Re: What is the value of x^3? [#permalink]

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13 Jun 2016, 23:04
1
KUDOS
Bunuel wrote:
What is the value of x^3?

(1) |x|=2
(2) 5x+6=16

Kudos for correct solution.

Statement 1

x = 2 or x = -2. Value of $$x^3$$ will be different in both cases. Not sufficient.

Statement 2

5x+6=16; 5x = 10; x = 2. We can get a unique value of $$x^3$$ from this. Sufficient.

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Manager
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Re: What is the value of x^3? [#permalink]

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11 Mar 2017, 18:50
MathRevolution wrote:
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 x^3?

(1) |x|=2
(2) 5x+6=16

In the original condition, there is 1 variable(x), which should match with the number of equations. So you need 1 equation. For 1) 1 equation, for 2) 1 equation, which is likely to make D the answer.
For 1), x^3=-8,8 is derived from x=-2,2, which is not unique and not sufficient.
For 2), 5x=10, x=3, x^3=8 is derived, which is unique and sufficient.

 For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.

Thanks for sharing. But how is ti different from the conventional method?

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Re: What is the value of x^3? [#permalink]

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06 Dec 2017, 03:24
Bunuel wrote:
What is the value of x^3?

(1) |x|=2
(2) 5x+6=16

Kudos for correct solution.

Statement 1. |x|=2 , x can be either -2 or 2.
Therefore x^3 can have two values, 8 or -8.
Hence insufficient.

Statement 2.
Solving 5x +6 =16 will yield only one value of X
Therefore statement two is sufficient.

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Re: What is the value of x^3?   [#permalink] 06 Dec 2017, 03:24
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