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Need help on a GMAT problem

by MonicaKhan » Fri Apr 20, 2007 11:26 am
For all positive integers m, m* = 3m, when m is odd and m* = (1/2)m when m is even. Which of the following is equivalent to 9* x 6*?

A) 81
B) 54
C) 36
D) 27
E) 18

I just can't figure this one out! The answer is D, but I don't understand why. Any help would be appreciated.
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Re: Need help on a GMAT problem

by jayhawk2001 » Fri Apr 20, 2007 5:37 pm
MonicaKhan wrote:For all positive integers m, m* = 3m, when m is odd and m* = (1/2)m when m is even. Which of the following is equivalent to 9* x 6*?

A) 81
B) 54
C) 36
D) 27
E) 18

I just can't figure this one out! The answer is D, but I don't understand why. Any help would be appreciated.
Whats the source for this problem ?

9* = 27 and 6* = 3. So, I'm not sure how it can be D
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by MonicaKhan » Fri Apr 20, 2007 8:42 pm
It was on one of my practice exams on the GMATPrep CD. SO bizaare!
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by Cybermusings » Sat Apr 21, 2007 1:38 am
For all positive integers m, m* = 3m, when m is odd and m* = (1/2)m when m is even. Which of the following is equivalent to 9* x 6*?

A) 81
B) 54
C) 36
D) 27
E) 18

9* (here m is odd) = 3*9=27
6* (here m is even) = 1/2*6=3
So answer = 27 times 3 = 81
Hence A
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by vinviper1 » Mon May 12, 2008 10:19 am
tricky one. Tha answer is 27. Not sure exactly one. One train of thought is 9*6 = 54 and therefore 54 * .5 equals 27. Any other thoughts?
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by jscoligan » Mon May 12, 2008 10:37 am
Answer should be A
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by II » Mon May 12, 2008 11:16 am
The question (or more precisely the answer choices) are not posted correctly.
See the screenshot, on how the question actually appears. This should make things clearer on why the answer choice is 27.
Attachments
For all positive integers m.jpg
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by rros0770 » Mon May 12, 2008 11:35 am
Good catch with that one II, its clear now
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by vinviper1 » Mon May 12, 2008 11:40 am
Can you guys lay out how you got to the answer? I want to confirm my work listed above. Thanks much.
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by rros0770 » Mon May 12, 2008 12:13 pm
The trick was in the answer choices. If you look at the answer choices that II posted, they are all 'boxed' just like M is in the main question.

In monicaKhan's original question '*' were used in place of the 'box', but the '*' should have been put next to all of the answer choices also, because they fall under the parameters of the function.

So all of us were getting '81' and not understanding how it was '27,' this is how:

9 is odd so it's-- 3(9)
6 is even so it--- 6/2

so 9*x6*=

3(9) x (6/2)=

27x 3=

81

Now, to get the correct answer apply the rules to the answer choices:

27* is 3(27)= 81...Answer choice (A) is really 81*, which would be equal to 243.

Choose D


Hope that helped
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by II » Mon May 12, 2008 12:41 pm
rros0770 wrote:The trick was in the answer choices. If you look at the answer choices that II posted, they are all 'boxed' just like M is in the main question.

In monicaKhan's original question '*' were used in place of the 'box', but the '*' should have been put next to all of the answer choices also, because they fall under the parameters of the function.

So all of us were getting '81' and not understanding how it was '27,' this is how:

9 is odd so it's-- 3(9)
6 is even so it--- 6/2

so 9*x6*=

3(9) x (6/2)=

27x 3=

81

Now, to get the correct answer apply the rules to the answer choices:

27* is 3(27)= 81...Answer choice (A) is really 81*, which would be equal to 243.

Choose D


Hope that helped
Great summary !
This is a tricky question ... and GMAC have many traps in this questions.
The key is to read the question carefully ... tough when you are under time pressure and stress. Question is asking "which is EQUIVALENT" ... this is the key part of the question.
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by vinviper1 » Mon May 12, 2008 12:59 pm
Thanks. And its great when they give you this trickery on question 3!

What confuses me a bit is that they say when m (not boxed) is odd. But we are looking at boxed figures in the beginning (9 and 6)
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by vinviper1 » Tue May 27, 2008 9:16 am
bumpy bump
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by alexdallas » Sat Jul 18, 2009 8:39 am
darn

tricky as heck this one :|
finally got it...thanks all!
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