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Sub 505 Level|   Algebra|   Exponents|                           
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x is positive; x^5 = ?

St1: sqrt(x) = 2^5
x = 2^10
x^5 = (2^10)^5 = 2^50
Sufficient

St2: x^2 = 2^20
x = 2^10
x^5 = 2^50
Sufficient

Answer: D
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Bunuel
If x > 0, what is the value of x^5 ?

(1) \(\sqrt{x}=32\)
(2) x^2 = 2^20


IMO D
Given x>0

From statement 1
Squaring x=2^10
x^5=2^50 Sufficient

From statement 2
x^2=2^20 implies x=2^10
x^5=2^50 Sufficient
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IMO D must be the answer.
1. √x=32 -->x=32^2 (since √x=|x| and hence always positive) . Therefore x^5=32^10. Sufficient
2. x^2 = 2^20 --> x=+2^10 or -2^10. Since x>0--> x^5 will be positive. Sufficient.
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In my opinion the correct answer is D.
(1) would be sufficient even if we didn't know that x is positive.
(2) is sufficient because we have x positive.
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Bunuel
If x > 0, what is the value of x^5 ?

(1) \(\sqrt{x}=32\)
(2) x^2 = 2^20
Hey Bunuel,

Just wanted to understand that in Statement 2 when we are taking the square root, why can't the right side of the equation take 2 values of +/- underoot 2^20?
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Bunuel
If x > 0, what is the value of x^5 ?

(1) \(\sqrt{x}=32\)
(2) x^2 = 2^20
Hey Bunuel,

Just wanted to understand that in Statement 2 when we are taking the square root, why can't the right side of the equation take 2 values of +/- underoot 2^20?

Check the highlighted part above.
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Bunuel
If x > 0, what is the value of x^5?


(1) \(\sqrt{x} =32\)

(2) \(x^2 = 2^{20}\)


NEW question from GMAT® Quantitative Review 2019


(DS05172)


Note : x is positive.

Statement 1:

\(\sqrt{x} =32\)

\(x = 32^2\)

\(x^5 = (32^2)^5\)

Sufficient.

Statement 2:

\(x^2 = 2^{20}\)

x^2 = 2^10^2

\(x = 2^{10}\)

x^5 = 2^10^5

Sufficient .

The best answer is D.
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x^5 = ?

(1) \(\sqrt{x} =32\)
\(\sqrt{x} =2^5\)
Squaring we get
x = 2^10
Since x is Positive, x^5 gives unique value
Sufficient

(2) \(x^2 = 2^{20}\)
x = 2^10
Since x positive, x^5 gives unique value
Sufficient

Hence, D.
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sudarshan22
x^5 = ?

(1) \(\sqrt{x} =32\)
\(\sqrt{x} =2^5\)
Squaring we get
x = 2^10
Since x is Positive, x^5 gives unique value
Sufficient

(2) \(x^2 = 2^{20}\)
x could be negative or positive, and that gives two values of x^5
Insufficient

Hence, A.


x>0. given in the question bro.
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selim
sudarshan22
x^5 = ?

(1) \(\sqrt{x} =32\)
\(\sqrt{x} =2^5\)
Squaring we get
x = 2^10
Since x is Positive, x^5 gives unique value
Sufficient

(2) \(x^2 = 2^{20}\)
x could be negative or positive, and that gives two values of x^5
Insufficient

Hence, A.

x>0. given in the question bro.
Holy crap! You are right :(
I hope that does not happen on D-Day.
Thanks for rectifying the blunder selim
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Hey Bunuel, one silly doubt: what root4 will yield, only +2 or +/- 2 :roll:
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Rhl5084
Hey Bunuel, one silly doubt: what root4 will yield, only +2 or +/- 2 :roll:

\(\sqrt{4}=2\) only, not +2/-2.

When the GMAT provides the square root sign for an even root, such as a square root, fourth root, etc. then the only accepted answer is the non-negative root. That is:

\(\sqrt{9} = 3\), NOT +3 or -3;
\(\sqrt[4]{16} = 2\), NOT +2 or -2;

Notice that in contrast, the equation \(x^2 = 9\) has TWO solutions, +3 and -3. Because \(x^2 = 9\) means that \(x =-\sqrt{9}=-3\) or \(x=\sqrt{9}=3\).
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Bunuel, thanks !

that helps :)
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