gmat prep problem

[dbart06]

HI! new to forum.

this problem has symbols. The problem reads:

for all positive integers, M=3m when m is odd, M=1/2m when m is even, which is equivalent to 9*6. remember M has a square around it as well as the 9 & 6. sorry, i wasnt able to screen shot. any help would be appreciated.

[Nycgrl]

can you please restate the problem

U can use ^ for square like for 3sqr 3^ 2

It will make it easy to understand.

Thanks

[dbart06]

for all positive integers, [M]=3m when m is odd, [M]=1/2m when m is even, which is equivalent to [9]*[6].

a)81
b)54
c)37
d)27
e)18

sorry for the confusion.

[Nycgrl]

No problems even I had problems with signs when I was new

Is it B???

[dbart06]

oa = d 27

[Ian Stewart]

for all positive integers, [M]=3m when m is odd, [M]=1/2m when m is even, which is equivalent to [9]*[6].

a)81
b)54
c)37
d)27
e)18

sorry for the confusion.

That's not quite what the question says, if I remember this correctly from GMATPrep. The answer choices should be:

a) [81]
b) [54]
c) [37]
d) [27]
e) [18]

We know [m]=3m when m is odd, [m]=(1/2)*m when m is even. Thus:
[9] = 3*9 = 27
[6] = 6/2 = 3

and [9]*[6] = 27*3 = 81. This often leads people to choose answer choice A, but notice that answer choice A is not equal to 81. The [] function is applied to each answer as well; answer choice A is [81] = 3*81 = 243. D is the correct answer, because [27] = 3*27 = 81 = [9]*[6].

[dbart06]

Thanks so much! It can be frustrating to be told you answered a question wrong with no explanation.

[medea66]

I just came across this problem in GPREP1 as well, and yes Ian, these guys are really out to get us.

[pre-gmat]

I think the problem can be solved much easily.

[9]*[6] is essentially [54] and this is an even number so as per the question M=1/2 m when m is even.

1/2 *[54] =27

Let me know if my reasoning is wrong.

[Ian Stewart]

I think the problem can be solved much easily.

[9]*[6] is essentially [54] and this is an even number so as per the question M=1/2 m when m is even.

1/2 *[54] =27

Let me know if my reasoning is wrong.

You cannot multiply through functions in the way you're attempting to do- that is, f(x)*f(y) is not normally equal to f(x*y). [9]*[6] is not equal to [54], and is not equal to 27; as described above, it is equal to [27], or 81.

[pre-gmat]

Thanks for making the concept clear.

[650 or bust]

Hello,

I'm new to the forum, too. I have a quick question...

I got to the point that 81 was the answer, but... how do we know when to stop? [81]=3m and m=27. How do we know that the GMAT testers aren't carrying it again? Or throwing in another trick?

Any ideas?

By the way, the explanations on this forum are EXCELLENT! Thank you!

[Abdulla]

I fell in the same trap today..

[ironsferri]

Hi everyone,

I don't quite get why to substitute 9 and 6 in the m, and not solve for m.
In specific,

[9] = 3*9 = 27
[6] = 6/2 = 3

I think [9] goes where [M] is, and not also in place of m. Therefore

[9] = 3*m
m = 3

The same with [6]

[6] = m*/2
m = 12

Can somebody advise?

Thank you so much