No M's in Algebra : GMAT Problem Solving (PS)
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# No M's in Algebra

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Manager
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10 Jun 2011, 17:44
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If m = 4

After solving the question it would become (1/2) / 14 so it should become 14 / 2 = 7

Somehow MGMAT says that 14 will be multiplied by 2 and the answer should be 1/28.
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 18:21
melguy wrote:
If m = 4

After solving the question it would become (1/2) / 14 so it should become 14 / 2 = 7

Somehow MGMAT says that 14 will be multiplied by 2 and the answer should be 1/28.

hi,
if you solve the equation you get -
$$\frac{m^2-2m-3m-6}{m(m+3)(m-2)}$$= $$\frac{(m-3)(m-2)}{m (m+3)(m-2)}$$= $$\frac{(m-3)}{m(m+3)}$$
Substituting m = 4 in above solved eqn
we get $$\frac{1}{28}$$
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 18:37
agdimple333 wrote:
melguy wrote:
If m = 4

After solving the question it would become (1/2) / 14 so it should become 14 / 2 = 7

Somehow MGMAT says that 14 will be multiplied by 2 and the answer should be 1/28.

hi,
if you solve the equation you get -
$$\frac{m^2-2m-3m-6}{m(m+3)(m-2)}$$= $$\frac{(m-3)(m-2)}{m (m+3)(m-2)}$$= $$\frac{(m-3)}{m(m+3)}$$
Substituting m = 4 in above solved eqn
we get $$\frac{1}{28}$$

agdimple333, my equation reduced to the same as yours. And substituting m = 4 into the equation also yields 1/28.

melguy, are there other constraints or information given for the question?

The part I don't get is why is m = 4?
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 18:53
Will you post the complete Q?

The way you have written the Q, it looks like it is given that m=4 and they are asking to find the value of the eqn.
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 18:56
agdimple333 wrote:
Will you post the complete Q?

The way you have written the Q, it looks like it is given that m=4 and they are asking to find the value of the eqn.

Right???? Because with the reduced equation you and I both got, technically you can plug in any damn number you want and it will still yield a solution...
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 18:57
Except for M = -3 or M = 0 of course.
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 20:02
agdimple333 wrote:
Will you post the complete Q?

The way you have written the Q, it looks like it is given that m=4 and they are asking to find the value of the eqn.

I posted the whole Q (except answer choices).

I just picked m=4 as a random number as per strategy in MGMAT FDP. Hope that clarifies.
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 20:10
Oh in that case it is A. The formula reduces to (m-3) / (M^2+3M)

Hope this helps.
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 20:13
melguy wrote:
agdimple333 wrote:
Will you post the complete Q?

The way you have written the Q, it looks like it is given that m=4 and they are asking to find the value of the eqn.

I posted the whole Q (except answer choices).

I just picked m=4 as a random number as per strategy in MGMAT FDP. Hope that clarifies.

yeh thats why it was confusing. I dont think i will put the numbers here, (i will check in MGMAT what are they trying to say)... but if you just solve the equation (i have solved in my post reply above) you will get answer which is choice A.
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 20:20
Yay. mystery solved!
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 20:34

I believe i did a simple multiplication incorrectly earlier. Please correct me if i am wrong.

In the example i) 1 will be multiplied by 4 which is understood

in example ii) if there is only one digit in the fraction we would multiply 2 x 3 (boxed numbers) and not 1.

thank u
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 20:36
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melguy wrote:
If m = 4

After solving the question it would become (1/2) / 14 so it should become 14 / 2 = 7

Somehow MGMAT says that 14 will be multiplied by 2 and the answer should be 1/28.

There is a big difference between (1/2) / 14 and 1/ (2/14). When you found the value 7 above, you were working out what 1/(2/14) was equal to: when we divide by a fraction, we multiply by its reciprocal, so 1/(2/14) = 1*(14/2) = 7.

That is not equal to (1/2)/14. Here, we can think of our denominator, 14, as being equal to the fraction 14/1. To divide by 14/1 we multiply by its reciprocal, so (1/2)/14 = (1/2)*(1/14) = 1/28.
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 20:37
Yes that is correct. In the case of (1/2) / 3. The actual multiplication would be (1/2)*(1/3).

Think of 3 as a stand alone integer. So if you need to divide something such as 6 by 3, then in essence, you are figuring out what is 1/3 of 6, which would be 6*(1/3).
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 20:40
IanStewart wrote:
melguy wrote:
If m = 4

After solving the question it would become (1/2) / 14 so it should become 14 / 2 = 7

Somehow MGMAT says that 14 will be multiplied by 2 and the answer should be 1/28.

There is a big difference between (1/2) / 14 and 1/ (2/14). When you found the value 7 above, you were working out what 1/(2/14) was equal to: when we divide by a fraction, we multiply by its reciprocal, so 1/(2/14) = 1*(14/2) = 7.

That is not equal to (1/2)/14. Here, we can think of our denominator, 14, as being equal to the fraction 14/1. To divide by 14/1 we multiply by its reciprocal, so (1/2)/14 = (1/2)*(1/14) = 1/28.

Thank you!!!

Silly error on my part.. I am too panicked..making basic mistakes... exam in 15 days....
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Re: No M's in Algebra [#permalink]

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10 Jun 2011, 20:44
I do the same thing. You just got to remind yourself to calm down. I found that when i tap my noise with a finger, it helps me refocus and think (but that is probably just because I am weird).
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Re: No M's in Algebra   [#permalink] 10 Jun 2011, 20:44
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