pluging in problem

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Gurpinder: Legendary Member; Posts: 659; Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members; Thanked: 32 times

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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Source: Beat The GMAT — Problem Solving | Wed Jul 14, 2010 12:09 pm

outreach: Legendary Member; Posts: 748; Joined: Sun Jan 31, 2010 7:54 amFollowed by: 3 members; Thanked: 46 times

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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Gurpinder: Legendary Member; Posts: 659; Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members; Thanked: 32 times

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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outreach: Legendary Member; Posts: 748; Joined: Sun Jan 31, 2010 7:54 amFollowed by: 3 members; Thanked: 46 times

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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https://amarnaik.wordpress.com
MBA blog
https://amarrnaik.blocked/

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Gurpinder: Legendary Member; Posts: 659; Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members; Thanked: 32 times

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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outreach: Legendary Member; Posts: 748; Joined: Sun Jan 31, 2010 7:54 amFollowed by: 3 members; Thanked: 46 times

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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https://amarnaik.wordpress.com
MBA blog
https://amarrnaik.blocked/

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

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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Gurpinder: Legendary Member; Posts: 659; Joined: Mon Dec 14, 2009 8:12 amFollowed by: 3 members; Thanked: 32 times

by Gurpinder » Wed Jul 14, 2010 1:17 pm

got it.....thanks guys

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