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# Did this on the GMATprep - and I swear I got it right, but

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Manager
Joined: 25 Aug 2007
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Did this on the GMATprep - and I swear I got it right, but [#permalink]  25 Aug 2007, 18:35
Did this on the GMATprep - and I swear I got it right, but the original answer suggests differently.

2^(4-1)^2 / 2^(3-2)

A. 2^8
B. 2^7
C. 2^6
D. 2^5
E. 2^4

I'm convinced that my answer is D (highlight to see)

But the OA is A (highlight to see)...
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VP
Joined: 10 Jun 2007
Posts: 1463
Followers: 6

Kudos [?]: 143 [0], given: 0

Re: Question on exponentials [#permalink]  25 Aug 2007, 19:36
Big-O wrote:
Did this on the GMATprep - and I swear I got it right, but the original answer suggests differently.

2^(4-1)^2 / 2^(3-2)

A. 2^8
B. 2^7
C. 2^6
D. 2^5
E. 2^4

I'm convinced that my answer is D (highlight to see)

But the OA is A (highlight to see)...

You can think of this two way, which are totally different. Let's just consider the top part...
2^(4-1)^2
This can be seen as: (2^3)^2 = 2^6
OR
2^(3^2) = 2^9
The latter will give you the right answer. I imagine in GMATprep, it should be pretty clear. Do you have a snapshot of the problem?
Manager
Joined: 25 Aug 2007
Posts: 70
Schools: HBS '10
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Here is the screenshot (I haven't been around enough to directly hotlink

A^B^C is the same as A^BC, therefore the top gives 2^6, not 2^9...
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Question.JPG [ 4.06 KiB | Viewed 567 times ]

VP
Joined: 08 Jun 2005
Posts: 1146
Followers: 6

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edited post

Its a simple case of BEDMAS

2^3^2 = 2^(3^2) = 512

not (2^3)^2 = 64

Don't check this in Excel spreadsheet. Excel will yield 64 for 2^3^2 this is wrong !

Last edited by KillerSquirrel on 25 Aug 2007, 23:49, edited 2 times in total.
VP
Joined: 10 Jun 2007
Posts: 1463
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Kudos [?]: 143 [0], given: 0

Thanks for the shot. I would have get 2^9 for the top, but I agree it is a bit unclear.
VP
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see edited post above !

Last edited by KillerSquirrel on 25 Aug 2007, 23:48, edited 1 time in total.
VP
Joined: 10 Jun 2007
Posts: 1463
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Kudos [?]: 143 [0], given: 0

KillerSquirrel wrote:
bkk145 wrote:
Thanks for the shot. I would have get 2^9 for the top, but I agree it is a bit unclear.

I see the operation of (4-1)^2 = 9 first.
Otherwise, I feel that there should have been parenthesizes like this:
(2^(4-1))^2
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