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symbols - source: gmat prep

by jsasipriya » Mon Aug 16, 2010 3:56 pm
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

OA D

This appears simple. But I'm not getting the OA. Can someone help pl.?
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by beatthegmatinsept » Mon Aug 16, 2010 4:10 pm
jsasipriya 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
OA D
This appears simple. But I'm not getting the OA. Can someone help pl.?
(9) X (6)
Since (9) is odd, then when m is odd, (m) = 3m. So (9) = 3*9 = 27.
Since (6) is even, then when (m) is even, (m) = 6/2 = 3.
(9) * (6) = 27 * 3 = 81
Since (81) is odd, using the same (m) = 3m, you get m = 81/3 = 27. [D]
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by jsasipriya » Mon Aug 16, 2010 4:21 pm
thanks!

But, can you tell me why is that we cannot stop after we get 81?
Why do you do the last step? I don't understand this part. pl help.
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by Tani » Mon Aug 16, 2010 7:36 pm
I agree - why would we need 2 iterations? In fact, why wouldn't the second iteration (m) = 3m be (81) = 3x81 = 243?

What is the source for this problem?
Tani Wolff
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by selango » Mon Aug 16, 2010 9:00 pm
jsasipriya,

The answers ll be in Symbol [] format.

So we need to represent 81 in [] format which is [27].
--Anand--
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by beatthegmatinsept » Mon Aug 16, 2010 9:26 pm
Tani Wolff - Kaplan wrote:I agree - why would we need 2 iterations? In fact, why wouldn't the second iteration (m) = 3m be (81) = 3x81 = 243?

What is the source for this problem?
Its from GMAT Prep Test 1
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by beatthegmatinsept » Mon Aug 16, 2010 9:28 pm
selango wrote:jsasipriya,

The answers ll be in Symbol [] format.

So we need to represent 81 in [] format which is [27].
Interesting.. I understand it as 81 already being in [] format, and solving for m, by dividing 81 by 3 to get 27.
Since [m] = 3m, or [81] = 3(27)
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by Tani » Tue Aug 17, 2010 6:42 am
I see - but the post did not have the answers in symbol format.
Tani Wolff
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