If 2^x - 2^x-2=3(2^13), what is the value of X? A.9 B.11 : PS Archive
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# If 2^x - 2^x-2=3(2^13), what is the value of X? A.9 B.11

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If 2^x - 2^x-2=3(2^13), what is the value of X? A.9 B.11 [#permalink]

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25 Apr 2006, 04:50
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If 2^x - 2^x-2=3(2^13), what is the value of X?

A.9
B.11
C.13
D.15
E.17
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25 Apr 2006, 05:03
solving the given equation,

2^x (3/4) = 3 * (2^13)

x = 15
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25 Apr 2006, 05:54
klsrikanth wrote:
solving the given equation,

2^x (3/4) = 3 * (2^13)

x = 15

please explain how you got this equation and how to solve.

thanks
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25 Apr 2006, 05:56
I get
2^x (1/2) = 3(2^13)

2^x - 2^(x-2) = 3(2^13)
2^x - 2^x * 2^-2 = 3(2^13)
factor out 2^x:
2^x(1-1/2) = 3(2^13)
2^x(1/2) = 3(2^13)
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25 Apr 2006, 06:17
Argh. nevermind.
I get it now as klsrikanth explained
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25 Apr 2006, 06:40
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gvogelei wrote:
klsrikanth wrote:
solving the given equation,

2^x (3/4) = 3 * (2^13)

x = 15

please explain how you got this equation and how to solve.

thanks

Give equation 2^x - 2^x-2

takin 2^x common out of the equation

we get, 2^x ( 1- 2^(-2))

2^x (3/4)
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25 Apr 2006, 18:23
I get 15 as well
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25 Apr 2006, 19:18
OA is D.

Good Work....Thanks
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Re: PS - Exponents GMATPrep 2 [#permalink]

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25 Apr 2006, 20:38
gvogelei wrote:
If 2^x - 2^x-2=3(2^13), what is the value of X?

A.9
B.11
C.13
D.15
E.17

Here is my approach
{2^(x-2)}*{(2^2)-1}=3*(2^13)
2^(x-2)*3=3*2^13
2^(x-2)=2^13
x=15
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Re: PS - Exponents GMATPrep 2   [#permalink] 25 Apr 2006, 20:38
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# If 2^x - 2^x-2=3(2^13), what is the value of X? A.9 B.11

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