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Data Sufficiency: Symbol

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ellen.chung
 Post subject: Data Sufficiency: Symbol
 Post Posted: Thu Sep 10, 2009 2:09 am 
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Course Students


Posts: 4
I can't figure this one out... I keep getting D but the correct answer is A. (I looked for this answer in the 17 pages of the forum but couldn't find it, sorry if it's already been posted). The problem is:

The symbol (triangle, I'll use ^ for it) represents one of the four arithmetic operations: addition, subtraction, multiplication, and division. Is (5^6)^2 = 5^(6^2)?

(1) 5^6 = 6^5
(2) 2^0 = 2

The reason I got D is because:

(1) means that ^ can either be + or x. Both operations make the original equation in the question true, so this is sufficient.

(2) means that ^ can either b + or -. Both operations make the original equation in the question true as well, so this is sufficient.

I got D. But the correct answer is A... help? Thanks in advance!
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nitin_prakash_khanna
 Post subject: Re: Data Sufficiency: Symbol
 Post Posted: Thu Sep 10, 2009 4:44 am 
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Students


Posts: 68
I think you are missing something really small.

(5+6)+2 = 13 ; 5+(6+2) = 13 so its fine.

But
(5-6)-1 = -2 ; whereas 5-(6-2) = 1-4 = -3

so st 2 is not suffcient Hope you are not forgetting the PEMDAS rule, must solve the paranthesis first.
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ellen.chung
 Post subject: Re: Data Sufficiency: Symbol
 Post Posted: Thu Sep 10, 2009 4:52 am 
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Course Students


Posts: 4
Ohhhhh you're sooo right! Thank you for clearing that up!! Such a silly mistake, definitely good to rejog my memory. Thanks for putting it so nicely too. :)
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snipertrader
 Post subject: Re: Data Sufficiency: Symbol
 Post Posted: Sat Sep 12, 2009 12:13 pm 
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Students


Posts: 2
Small correction..

It should be (5-6)-2 = -3
whereas 5-(6-2) = 1

Cheers!

nitin_prakash_khanna wrote:
I think you are missing something really small.

(5+6)+2 = 13 ; 5+(6+2) = 13 so its fine.

But
(5-6)-1 = -2 ; whereas 5-(6-2) = 1-4 = -3

so st 2 is not suffcient Hope you are not forgetting the PEMDAS rule, must solve the paranthesis first.
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RonPurewal
 Post subject: Re: Data Sufficiency: Symbol
 Post Posted: Sat Sep 26, 2009 1:49 am 
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ManhattanGMAT Staff


Posts: 7146
ellen.chung wrote:
Ohhhhh you're sooo right! Thank you for clearing that up!! Such a silly mistake, definitely good to rejog my memory. Thanks for putting it so nicely too. :)


at the risk of sounding like a second grade teacher, here's the best way to avoid having this sort of problem again:
if the work on a problem is easy - such as doing arithmetic - then you should DO THE WORK.

even if you didn't remember that the associative rule doesn't apply to subtraction, you could just have executed the operations (5 - 6) - 2 and 5 - (6 - 2), and found that they were different.
don't let a problem slip out of your hands by lacking the diligence to subtract - especially after you've ALREADY done all the heavy lifting in the problem!
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