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pluging in problem

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pluging in problem

by Gurpinder » Wed Jul 14, 2010 12:09 pm
If 3a - b = c, then in terms of a, what is the average (arithmetic mean) of a, b and c?

3a
4a/3
a/3
a/2
a

???? i dont get this one guys....please help me out.
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by outreach » Wed Jul 14, 2010 12:12 pm
mean = (a+b+c)/3 - (1)

given eq 3a - b = c =>3a=b+c - (2)

sub 2 in 1

then mean=4a/3
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by Gurpinder » Wed Jul 14, 2010 12:18 pm
outreach wrote:mean = (a+b+c)/3 - (1)

given eq 3a - b = c =>3a=b+c - (2)

sub 2 in 1

then mean=4a/3
can you please explain outreach.
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by outreach » Wed Jul 14, 2010 12:19 pm
wht is not clear?
Gurpinder wrote:
outreach wrote:mean = (a+b+c)/3 - (1)

given eq 3a - b = c =>3a=b+c - (2)

sub 2 in 1

then mean=4a/3
can you please explain outreach.
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by Gurpinder » Wed Jul 14, 2010 12:21 pm
outreach wrote:wht is not clear?
Gurpinder wrote:
outreach wrote:mean = (a+b+c)/3 - (1)

given eq 3a - b = c =>3a=b+c - (2)

sub 2 in 1

then mean=4a/3
can you please explain outreach.
just how you would approach such a problem.

i started giving each variable a value....which didnt workout
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by outreach » Wed Jul 14, 2010 12:57 pm
let me try.hopefully i am helpful

when i solve such problems i first create all the eq based on data given in Q and then proceed

Q asked is what is the average (arithmetic mean) of a, b and c in terms of ?
average of a, b and c=(a+b+c)/3 (1)
but the Q asks the avg interms of 'a' only. so we need to represent b and c interms of a


in the Q another eq 3a - b = c is given. rearranging we get 3a=b+c (2)

solving 1 and 2 we get the solution
Gurpinder wrote:
outreach wrote:wht is not clear?
Gurpinder wrote:
outreach wrote:mean = (a+b+c)/3 - (1)

given eq 3a - b = c =>3a=b+c - (2)

sub 2 in 1

then mean=4a/3
can you please explain outreach.
just how you would approach such a problem.

i started giving each variable a value....which didnt workout
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by GMATGuruNY » Wed Jul 14, 2010 1:11 pm
Gurpinder wrote:If 3a - b = c, then in terms of a, what is the average (arithmetic mean) of a, b and c?

3a
4a/3
a/3
a/2
a

???? i dont get this one guys....please help me out.
We need to plug and chug. Plug in a=4, b=2. Now we plug these values into 3a - b = c into order to determine c.

3*4 - 2 = 12 - 2 = 10. So c = 10.

The question is asking for the average of the 3 values:

(4 + 2 + 10)/3 = 16/3. So our target answer is 16/3.

Now we plug a=4 into all the answer choices until we find the one that gives us 16/3. Only answer choice B works: 4a/3 = 4*4/3 = 16/3.
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by Gurpinder » Wed Jul 14, 2010 1:17 pm
got it.....thanks guys
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