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# A Simple but confusing DS [ 8^a(1/4)^b = ? ]

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Intern
Joined: 09 Oct 2008
Posts: 18
A Simple but confusing DS [ 8^a(1/4)^b = ? ]  [#permalink]

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17 Oct 2008, 01:43
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8^a(1/4)^b = ?

(1) b = 1.5a
(2) a = 2

Lets see how you guys solve it

--== Message from GMAT Club Team ==--

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If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Intern
Joined: 24 Jun 2007
Posts: 28
Re: A Simple but confusing DS [ 8^a(1/4)^b = ? ]  [#permalink]

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17 Oct 2008, 02:08
8^a(1/4)^b = ?
2^3a 2^-2b = ?
so 2^(3a-2b) = ?

(S1) b = 1.5a

then 2^ (3a - 2(1.5a)) = ?
2^ (3a-3a) =?
2^0= 1......Suff

(S2) a = 2
2^(3(2) - 2b) =?
still stuck with b .....then ...insuff

my thought is A
Intern
Joined: 09 Oct 2008
Posts: 18

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17 Oct 2008, 02:23
You are right paeagain.. the OA is (A)

But whats confusing me, upon solving we end up with:

8^a.(1/4)^b

2^(3a).2^(-2b)

3a-2b = ?

But isn't it same as the S(1) itself:

b = 1.5a
2b = 3a

and if we further see our original equation 3a-2b = ?
it tells us 3a = 2b which is what the statement (1) is. So is it solving the question.
I know how you will explain this as 3a-2b= 0 so its sufficient but that is exactly the same as question stem.
VP
Joined: 30 Jun 2008
Posts: 1004

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17 Oct 2008, 04:25
alive wrote:
You are right paeagain.. the OA is (A)

But whats confusing me, upon solving we end up with:

8^a.(1/4)^b

2^(3a).2^(-2b)

3a-2b = ?

But isn't it same as the S(1) itself:

b = 1.5a
2b = 3a

and if we further see our original equation 3a-2b = ?
it tells us 3a = 2b which is what the statement (1) is. So is it solving the question.
I know how you will explain this as 3a-2b= 0 so its sufficient but that is exactly the same as question stem.

This is a C-Trap question. Search this forum for more details on C-Trap.

The question asks what is the value of 3a-2b.

Statement 1 says the value of 3a-2b is zero.

You will come across such questions .... like is x=0? and one of the statements will be like x^2 + y^2 = 0 which clearly says x=0. It may sound simple, but many people like me will fail to see the logic and fall for the C-Trap.
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

Senior Manager
Joined: 21 Apr 2008
Posts: 265
Location: Motortown
Re: A Simple but confusing DS [ 8^a(1/4)^b = ? ]  [#permalink]

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17 Oct 2008, 04:57
I don't know whether I would think about C-Traps etc., but
2^(3a -2b) = ?

from statement 1 :
3a = 2b
2^(2b-2b) = 2^0 = 1

from statement 2:
a= 2 - won't help
VP
Joined: 30 Jun 2008
Posts: 1004
Re: A Simple but confusing DS [ 8^a(1/4)^b = ? ]  [#permalink]

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17 Oct 2008, 05:27
LiveStronger wrote:
I don't know whether I would think about C-Traps etc., but
2^(3a -2b) = ?

from statement 1 :
3a = 2b
2^(2b-2b) = 2^0 = 1

from statement 2:
a= 2 - won't help

Don't have to think about it Knowing doesn't hurt ....
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

Senior Manager
Joined: 21 Apr 2008
Posts: 265
Location: Motortown
Re: A Simple but confusing DS [ 8^a(1/4)^b = ? ]  [#permalink]

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17 Oct 2008, 06:37
Good one

Btw, can you explain more about C- Traps ?
VP
Joined: 30 Jun 2008
Posts: 1004
Re: A Simple but confusing DS [ 8^a(1/4)^b = ? ]  [#permalink]

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17 Oct 2008, 07:02
1
LiveStronger wrote:
Good one

Btw, can you explain more about C- Traps ?

Check this one first --- LONG ONE ---- http://gmatclub.com/forum/viewtopic.php?t=34329

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

Re: A Simple but confusing DS [ 8^a(1/4)^b = ? ] &nbs [#permalink] 17 Oct 2008, 07:02
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