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# 8)^-5/(0.4)^-4 = ? A. 3/32 B. 5/64 C. 1/2 D. 1 E. 2

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8)^-5/(0.4)^-4 = ? A. 3/32 B. 5/64 C. 1/2 D. 1 E. 2  [#permalink]  26 Oct 2007, 06:10
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(0.8)^-5/(0.4)^-4 = ?

A. 3/32
B. 5/64
C. 1/2
D. 1
E. 2

(From GWD - 30)

SVP
Joined: 01 May 2006
Posts: 1805
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(B) for me

(0.8)^-5/(0.4)^-4
= (2*0.4)^-5 / (0.4)^-4
= 2^-5 * (4/10)^-1 * (0.4)^-4 / (0.4)^-4
= 1/(2^5) * (10/4)
= 5*2 / (2 * 2^4 * 2^2)
= 5 / (2^3 * 2^3)
= 5 / (8*8)
= 5 / 64
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Joined: 10 Jun 2007
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Re: PS - Exponents [#permalink]  26 Oct 2007, 06:19
mistahfold wrote:
(0.8)^-5/(0.4)^-4 = ?

A. 3/32
B. 5/64
C. 1/2
D. 1
E. 2

(From GWD - 30)

(0.8^-5) / (0.4^-4) = (0.4^4) / (0.8^5) = (0.4^4) / ((2^5)*(0.4^5))
= 10 / (2^7) = 5 / 2^6 = 5/64
Intern
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Excellent you guys are on the mark. It's good exponent practice (I thought!) Thank you.
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Re: PS - Exponents [#permalink]  07 Apr 2008, 18:03
i know i made a mistake...but what did I do wrong?

1 / 8/10^5 / 1 / 4/10^4

10/8 / 10/4

= 1/2
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Re: PS - Exponents [#permalink]  07 Apr 2008, 19:26
giantSwan wrote:
i know i made a mistake...but what did I do wrong?

1 / 8/10^5 / 1 / 4/10^4

10/8 / 10/4

= 1/2

(8/10)^-5 != 1 / 8/10^5
(8/10)^-5 = 1/ (8^5)/(10^5)

(4/10)^-4 != 1 / 4/10^4
(4/10)^-4 = 1/ (4^4)/(10^4)
Re: PS - Exponents   [#permalink] 07 Apr 2008, 19:26
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