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GRE Math Challenge #2- (2^30 - 2^29)/2

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Director
Director
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Joined: 16 May 2014
Posts: 597
GRE 1: 326 Q165 V161
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GRE Math Challenge #2- (2^30 - 2^29)/2 [#permalink] New post 29 May 2014, 01:44
Expert's post
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

100% (01:12) correct 0% (00:00) wrong based on 13 sessions
Attachment:
2.JPG
2.JPG [ 19.04 KiB | Viewed 10129 times ]

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If you find this post helpful, please press the kudos button to let me know ! :)

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Intern
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Re: GRE Math Challenge #2 [#permalink] New post 24 Oct 2014, 18:54
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KUDOS
Quantity A

2^30 - 2^29/2
= 2^29(2^1 - 1)/2
= 2^29(2 - 1)/2
= 2^29(1)/2
= 2^29/2^1
= 2^28


Quantity B

2^28



[Reveal] Spoiler:
(C) The two quantities are equal
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Re: GRE Math Challenge #2 [#permalink] New post 18 May 2015, 14:59
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Expert's post
soumya1989 wrote:
Attachment:
2.JPG

My first (favorite) approach is the same as mclchu's.

However, I do have a second approach:
Let's use the technique of performing the same operation on each quantity. By the way, we have a free video on this strategy here: http://www.greenlighttestprep.com/module/gre-quantitative-comparison?id=1097

Quantity A: (2^30 - 2^29)/2
Quantity B: 2^28

Multiply both quantities by 2 to get:
Quantity A: 2^30 - 2^29
Quantity B: (2^28)(2^1) = 2^29

Add 2^29 to both quantities to get:
Quantity A: 2^30
Quantity B: 2^29 + 2^29

NOTE: adding the same quantity to itself is the same a multiplying that quantity by 2. For example, 7 + 7 = 2(7) and 11 + 11 = 2(11)
So, 2^29 + 2^29 = 2(2^29)

So, we get:
Quantity A: 2^30
Quantity B: 2(2^29) = (2^1)(2^29) = 2^30

Answer:
[Reveal] Spoiler:
C


Cheers,
Brent
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Re: GRE Math Challenge #2   [#permalink] 18 May 2015, 14:59
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GRE Math Challenge #2- (2^30 - 2^29)/2

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