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Intern  Joined: 27 May 2014
Posts: 1
If 11m − n = p, then which of the following represents the a  [#permalink]

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Question Stats: 89% (01:10) correct 11% (02:13) wrong based on 113 sessions

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If 11m − n = p, then which of the following represents the average (arithmetic mean) of m, n, and p, in terms of m?

(A) 2m −1
(B) 4m
(C) 6m
(D) m/5
(E) 6m/5

The answer is 4m, but I got 2m, what did I do wrong?
I got: p=11m-n 11m-n-p+11m+p+n\frac{}{11}=22/11m=2m

n=-p+11m

m=p+n/11

Originally posted by kennavalkyrie on 27 May 2014, 12:51.
Last edited by Bunuel on 27 May 2014, 13:31, edited 1 time in total.
Renamed the topic, edited the question, added the OA and moved to PS forum.
Magoosh GMAT Instructor G
Joined: 28 Dec 2011
Posts: 4472
Re: Arithmetic Mean Question  [#permalink]

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kennavalkyrie wrote:
If 11m-n=p, then which of the following represents the average of m, n, and p, in terms of m?

The answer is 4m, but I got 2m, what did I do wrong?
I got: p=11m-n 11m-n-p+11m+p+n\frac{}{11}=22/11m=2m

n=-p+11m

m=p+n/11

Dear kennavalkyrie,
I'm happy to respond. Unfortunately, the way you have presented your work is unclear enough that I cannot follow what you were thinking. I think part of the problem, in that last line, is that when you divide by 11, you need to divide every term. Relatedly, I think you are neglecting grouping symbols, and overlooking these core mathematical symbols leads to a large number of mistakes. See:
http://magoosh.com/gmat/2013/gmat-quant ... g-symbols/

I will show you the solution:
11m - n = p
Add n to both sides:
11m = n + p
Add m to both sides:
12m = n + p + m
Now, divide both sides by 3
4m = (n + p + m)/3 = the average of n, p, and m

Does all this make sense?
Mike _________________
Mike McGarry
Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)
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Joined: 02 Sep 2009
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Re: Arithmetic Mean Question  [#permalink]

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kennavalkyrie wrote:
If 11m-n=p, then which of the following represents the average of m, n, and p, in terms of m?

The answer is 4m, but I got 2m, what did I do wrong?
I got: p=11m-n 11m-n-p+11m+p+n\frac{}{11}=22/11m=2m

n=-p+11m

m=p+n/11

If 11m − n = p, then which of the following represents the average (arithmetic mean) of m, n, and p, in terms of m?

(A) 2m −1
(B) 4m
(C) 6m
(D) m/5
(E) 6m/5

The average of m, n, and p is $$\frac{m+n+p}{3}$$.

Since 11m − n = p, then n + p = 11m. Substitute the value of n + p into the average expression: $$\frac{m+n+p}{3}=\frac{m+11m}{3}=\frac{12m}{3}=4m$$.

P.S. Please read carefully and follow: rules-for-posting-please-read-this-before-posting-133935.html Pay attention to rules 1, 3, 5, and 8. Thank you.
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Posts: 4006
Re: If 11m − n = p, then which of the following represents the a  [#permalink]

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kennavalkyrie wrote:
If 11m − n = p, then which of the following represents the average (arithmetic mean) of m, n, and p, in terms of m?

(A) 2m −1
(B) 4m
(C) 6m
(D) m/5
(E) 6m/5

Another approach (similar to Bunuel's):

Average = (m + n + p)/3
Replace p with 11m - n, to get:
Average = [m + n + (11m - n)]/3
= 12m/3
= 4m

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Cheers,
Brent
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Re: If 11m − n = p, then which of the following represents the a  [#permalink]

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m+n+p/3
=m+n+11m-n/3
=12m/3
=4m

B
Intern  G
Joined: 21 May 2016
Posts: 27
Re: If 11m − n = p, then which of the following represents the a  [#permalink]

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Arithmetic mean=(m+n+p)/3
From the equation we have
11m-n=p
11m=p+n
Substituting the value pf p+n
AM=12m/3=4m
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Re: If 11m − n = p, then which of the following represents the a  [#permalink]

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kennavalkyrie wrote:
If 11m − n = p, then which of the following represents the average (arithmetic mean) of m, n, and p, in terms of m?

(A) 2m −1
(B) 4m
(C) 6m
(D) m/5
(E) 6m/5

We have the following expression for the average of m, n, and p:

(m + n + p)/3

Substituting (11m - n) for p, we obtain:

(m + n + 11m - n)/3 = 12m/3 = 4m

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If you find one of my posts helpful, please take a moment to click on the "Kudos" button. Re: If 11m − n = p, then which of the following represents the a   [#permalink] 27 Sep 2018, 17:35
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