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# 1/ 2^10 + 1/ 2^11 + 1/ 2^12 + 1/ 2^13=

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Eternal Intern
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1/ 2^10 + 1/ 2^11 + 1/ 2^12 + 1/ 2^13=  [#permalink]

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22 Jul 2003, 17:28
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1/ 2^10 + 1/ 2^11 + 1/ 2^12 + 1/ 2^13=

How to do this fast?

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Manager
Joined: 07 Jul 2003
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22 Jul 2003, 18:17
Do you really need it???

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Intern
Joined: 04 Jun 2003
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22 Jul 2003, 18:33
Find the common denominator, which is 2^13.

then it would be (2^3+2^2+2+1)/2^13=15/2^13

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Eternal Intern
Joined: 07 Jun 2003
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22 Jul 2003, 19:22
Why is 2 ^13, the common denominator, I didn't get 47 on my GMAT, nor am I predicted to get one, but aiming for 40 +

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SVP
Joined: 03 Feb 2003
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22 Jul 2003, 21:37
or take 2^10 as a common part

2^10 (1+1/2+1/4+1/8)=15/2^13

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Intern
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24 Jul 2003, 00:09
Curly,

2^13 is the common denominator because in this particular sequence, it is the largest number that is the multiple of the others.

For example, 1/2+1/4.... 4 is the common denominator when you add the fractions together: 2/4+1/4=3/4, and 4 is a multiple of 2.

Hope it helps.

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24 Jul 2003, 00:09
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