Subsitution question?

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Subsitution question?

by anthony.j » Sun May 03, 2009 11:41 am
Hi,

I thought this problem was a simple subsitution problem was I am unable to figure out how to solve for the correct answer

For all positive intergers, m, box around m = 3m when m is odd and box around m = m/2 when m is even. Which of the following is equivalent to box around 9 x box around 6?

When I reattempted the problem I set 9 = 3m which is 3 and 6 = 1/2M which is 12. then i multipled them together for 36. However, the correct answer is 27. What am i doing wrong?

Sorry I could not draw a box around the letter m or insert the pic into this window. If you need to see the problem, I attached it as a word doc. Thanks for your help.[/img]
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by cneal4 » Mon May 04, 2009 7:53 am
Hello,

For this problem you have to substitute whatever you value for M is into the equation 3M-odd or 1/2M-even

You was Given 9 as M and 6 as M

So you the formula tells you to substitute those values into the equation to get:

= [9]*3 times [6]*(1/2)

= 27 * 3

= 81

as you can see doing the same thing for [27] gives you 81 also.

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by anthony.j » Mon May 04, 2009 8:08 am
cneal4 wrote:Hello,

For this problem you have to substitute whatever you value for M is into the equation 3M-odd or 1/2M-even

You was Given 9 as M and 6 as M

So you the formula tells you to substitute those values into the equation to get:

= [9]*3 times [6]*(1/2)

= 27 * 3

Thanks for the feeback; however, the correct answer is per the GMAT is 27. I got the same answer as you but it is not correct. Could the test software be incorrect?

= 81

as you can see doing the same thing for [27] gives you 81 also.

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by anthony.j » Mon May 04, 2009 8:31 am
I found the correct way to solve this problem. Here is the link in case you want to know why the correct answer is 27

https://www.beatthegmat.com/please-expla ... 23590.html

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by Svedankae » Mon May 11, 2009 12:24 pm
hey anthony!

thanks for posting this question and the solution. unfortunately i still dont get it...... would you (or anyone else) try to explain to me why it is [27]?

i was absolutely certain that the answer should be 36 or [18] ...

thanks,

sven

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by anthony.j » Mon May 11, 2009 7:18 pm
The correct answer is 27.

The question is asking which of the following is equivalent to (9) x (6)

When (m) is odd, we use the formula (m) = 3m. Therefore 9 is odd and we plug it into the formula. We now have (m) = 3*9 = 27 for the first part of the equation.

The second part of the equation states if we have an even number we use (m) = 1/2(m). We now have (6)*1/2 = 3 for the second part of the equation.

Now we put both numbers into the formula and solve: 27 * 3 = 81. Here is tricky part. 81 is an odd number and the question asks you which of the numbers below is equivalent to (9) x (6).

Since 81 is odd, we need to find what number works with the original formula, m = 3m. Now you need to plug and solve. (81) = 3m. This equals 27 and solves the problem.

It took me a while to figure this problem out too. I hope this explanation helps.

Anthony