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9 is odd:  = 3*9 = 27 6 is even:  = (1/2)*6 = 3
Hence  x  = 27 x 3 = 81 Ans: A
My bad. The answers should have been worded as follows (which makes a difference).
When the answers are reworded, the correct answer is D, or . It looks like GMAC was tricky with this question and some readers didn't notice the answers were surrounded by a box. Fortunately, I was lucky enough to find a thread that discusses this:
Funny, I came across this questions today as well and I answered it the same way. It's not that 81 is wrong, it's that we chose the wrong answer. I think the asterisk represents a box, right? All of the answer choices were boxed, therefore we're still supposed to follow the rules mentioned in the question. 27* is right because 27 multiplied by 3 (the rule for odd integers) is 81.
The asterisk is a box! But I couldn't copy and paste so I had to come up with something Oh God, now I got it. You're soo right! I completely ignored the fact that the answers were in the box too. My bad. Thanks a lot! Did you look at my other post too? I have a feeling I'm ignoring something obvious in that one too! Thanks again!
hi guys, I can't figure out why I can't get this question right, appreciate all comments in advance.
Q: For all positive integers m, [m]=3m when m is odd and [m]=1/2 m when m is even. What is  x  equivalent to?
1)  2)  3)  4)  5) 
now my answer was 81 but the right answer according to Official GMAT is 27 and I can't seem to understand why! please help me out here.
Because [m] = 3m when m is odd, =3m, m=3. Using the same logic for , =3 3*3=9 If you put this back in [m] form you get 3*9= (we must use 3m because m is odd, if it were even it would be .5*9) Thus answer choice C
Re: Tough Algebra, Can anyone help me? Thanks!! [#permalink]
08 Feb 2010, 14:52
This post received KUDOS
We know that  = 3*9 = 27, since [x] = 3x when x is odd. We also know that  = 3, since [x] = x/2 when x is even. So * = 27*3 = 81.
Now, many people choose the wrong answer to this question, despite doing all of the work correctly, because they do not notice that the answer choices are all in boxes - a devious GMAT trap. So the answer choice which reads  is not equal to the number 81; it is equal to 3*81 = 243, because [x] = 3x when x is odd. The correct answer here is , which is equal to the number 81. _________________
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