Arithmetic Mean Doubt

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goelmohit2002: Legendary Member; Posts: 1799; Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members; Thanked: 36 times

by goelmohit2002 » Fri Mar 27, 2009 7:34 am

Hi All,

I will post OA after some discussion...so that other fellow members reasoning is not biased by OA.

The results of a certain experiment included 6 data values that were all multiples of the same number c, namely, c, 8c, 2c, 5c, 4c, and 4c. Was the average (arithmetic mean) of the 6 data values greater than 8?
(1) c < 4
(2) c > 2

Thanks
Mohit

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Source: Beat The GMAT — Data Sufficiency | Fri Mar 27, 2009 7:34 am

scoobydooby: Legendary Member; Posts: 1035; Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member; Thanked: 104 times

by scoobydooby » Fri Mar 27, 2009 8:02 am

AM: (c+8c+2c+5c+4c+4c)/6=24c/6=4c

1) c<4
if c=3, AM=4*3=12 > 8
if c-1, AM=4*1=4 <8
not sufficient

2) c>2
if c=2, AM=4*2=8
so if c>2, AM >8
sufficient

hence B

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goelmohit2002: Legendary Member; Posts: 1799; Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members; Thanked: 36 times

by goelmohit2002 » Fri Mar 27, 2009 8:10 am

yes got it....i made a calculation mistake of dividing by 8...while calculating average...

Yes the OA is "B".

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goelmohit2002: Legendary Member; Posts: 1799; Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members; Thanked: 36 times

by goelmohit2002 » Fri Mar 27, 2009 8:16 am

Can someone please help me in resolving one small doubt?

The above statement says: "all multiples of the same number c".

can we assume by this statement that "c" is integer....or there can be multiples of real number too.

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

by Ian Stewart » Fri Mar 27, 2009 9:11 am

goelmohit2002 wrote:Can someone please help me in resolving one small doubt?

The above statement says: "all multiples of the same number c".

can we assume by this statement that "c" is integer....or there can be multiples of real number too.

We typically only use the term 'multiple' when dealing with integers. In a real GMAT question, this would normally be stated explicitly - were the question in the original post above a real GMAT question, I'd expect it to say that c is an integer.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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goelmohit2002: Legendary Member; Posts: 1799; Joined: Wed Dec 24, 2008 3:03 amFollowed by: 2 members; Thanked: 36 times

by goelmohit2002 » Fri Mar 27, 2009 10:16 am

I am not sure whether this is a real GMAT question....but this is one of the VIP tests question....

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