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# What is the value of x?

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Math Expert
Joined: 02 Sep 2009
Posts: 53020
What is the value of x?  [#permalink]

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16 Jul 2017, 22:10
00:00

Difficulty:

85% (hard)

Question Stats:

43% (02:42) correct 57% (01:53) wrong based on 72 sessions

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What is the value of x?

(1) $$4^x − 20*2^x + 64 = 0$$

(2) $$4^x = x^4$$

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Math Expert
Joined: 02 Aug 2009
Posts: 7334
Re: What is the value of x?  [#permalink]

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17 Jul 2017, 00:11
Bunuel wrote:
What is the value of x?

(1) $$4^x − 20*2^x + 64 = 0$$

(2) $$4^x = x^4$$

Hi...

Lets see the statements..
(1) $$4^x − 20*2^x + 64 = 0$$
To solve this let's take $$2^x=a$$..
So $$a^2-20a+64=0........(a-16)(a-4)=0$$..
So a=16 or a=4..
Or $$2^x=16...X=4.......2^x=4..X=2$$
Two values, 2 and 4 possible
Insufficient

(2) $$4^x = x^4$$
Clearly x cantake value of 2 or 4..
Insuff

Combined
X as 2 or 4 still exists
Insufficient

E
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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html
4) Base while finding % increase and % decrease : https://gmatclub.com/forum/percentage-increase-decrease-what-should-be-the-denominator-287528.html

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

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28 Jan 2019, 22:01
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: What is the value of x?   [#permalink] 28 Jan 2019, 22:01
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