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For which of the following options is the average (arithmetic mean) of

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Math Revolution GMAT Instructor
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For which of the following options is the average (arithmetic mean) of [#permalink]

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New post 11 Sep 2017, 00:29
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

60% (01:50) correct 40% (01:29) wrong based on 60 sessions

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[GMAT math practice question]

I. 9/10, 10/11, 11/12, 12/13, 13/14
II. 10/9, 11/10, 12/11, 13/12, 14/13
III. 6/10, 7/10, 8/10, 9/10, 10/10

For which of the following options is the average (arithmetic mean) of the numbers less than the median of numbers?

A. I. only
B. II. only
C. III. only
D. II and III
E. I, II and III

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Re: For which of the following options is the average (arithmetic mean) of [#permalink]

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New post 11 Sep 2017, 03:07
Since III has a average = median = 8/10, it can be eliminated!
Hence, Option C,D and E are wrong!

So, the answer is either Option A or Option B.

Lets consider the set - 9/10, 10/11, 11/12, 12/13, 13/14
The median is 11/12 = 0.9167
The mean is 0.9 + 0.909 + 0.916 + 0.923 + 0.929 = 4.57/5 = approximately 0.9154
Here, the average is lesser than the median(Option A)
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Math Revolution GMAT Instructor
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Re: For which of the following options is the average (arithmetic mean) of [#permalink]

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New post 13 Sep 2017, 00:16
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3
=>

I. Differences between consecutive terms are 10/11 – 9/10 = 1/110, 11/12 – 10/11 = 1/132, 12/13 – 11/12 = 1/156, 13/14 – 12/13 = 1/182. The differences are getting smaller. The average is smaller than the median.

II. Difference between consecutive terms are 11/10 – 10/9 = -1/90, 12/11 – 11/10 = -1/110, 13/12 – 12/11 = -1/132, 14/13 – 13/12 = -1/156. The differences are getting bigger. The average is bigger than the media.

II Difference between consecutive terms are 7/10 – 6/10 = 1/10, 8/10 – 7/10 = 1/10, 9/10 – 8/10 = 1/10, 10/10 – 9/10 = 1/10. All differences are equal. The average is equal to the median.

Ans: A
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Re: For which of the following options is the average (arithmetic mean) of [#permalink]

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New post 13 Sep 2017, 11:04
I. 9/10, 10/11, 11/12, 12/13, 13/14
II. 10/9, 11/10, 12/11, 13/12, 14/13
III. 6/10, 7/10, 8/10, 9/10, 10/10

For which of the following options is the average (arithmetic mean) of the numbers less than the median of numbers?

A. I. only
B. II. only
C. III. only
D. II and III
E. I, II and III

In the above question, I know to quickly eliminate choices C, D, and E as each references III which has an average = median.

My question: Is there an quicker way to identify between the correct answer A or B other than setting the fractions equal, adding, averaging, and then comparing against the median? I.E. How do I quickly identify the right answer between A and B so I manage time effectively?
Expert Post
Math Revolution GMAT Instructor
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Joined: 16 Aug 2015
Posts: 5574
GMAT 1: 800 Q59 V59
GPA: 3.82
Re: For which of the following options is the average (arithmetic mean) of [#permalink]

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New post 13 Sep 2017, 11:57
gblessing wrote:
I. 9/10, 10/11, 11/12, 12/13, 13/14
II. 10/9, 11/10, 12/11, 13/12, 14/13
III. 6/10, 7/10, 8/10, 9/10, 10/10

For which of the following options is the average (arithmetic mean) of the numbers less than the median of numbers?

A. I. only
B. II. only
C. III. only
D. II and III
E. I, II and III

In the above question, I know to quickly eliminate choices C, D, and E as each references III which has an average = median.

My question: Is there an quicker way to identify between the correct answer A or B other than setting the fractions equal, adding, averaging, and then comparing against the median? I.E. How do I quickly identify the right answer between A and B so I manage time effectively?


Please take a look at the above solution from Math Revolution.
We can compare the average and the median using differences between consecutive terms.

Happy Studying !!!
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
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"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Re: For which of the following options is the average (arithmetic mean) of   [#permalink] 13 Sep 2017, 11:57
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For which of the following options is the average (arithmetic mean) of

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