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# A certain set of test scores has an average (arithmetic mean) of 70 an

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Math Expert
Joined: 02 Sep 2009
Posts: 54369
A certain set of test scores has an average (arithmetic mean) of 70 an  [#permalink]

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10 Oct 2016, 00:46
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15% (low)

Question Stats:

79% (01:37) correct 21% (02:20) wrong based on 89 sessions

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A certain set of test scores has an average (arithmetic mean) of 70 and a standard deviation of 25. If m and n, two numbers in the set, are both within 2 standard deviations from the average, then which of the following could be the average of m and n?

A. 10
B. 14
C. 17
D. 19
E. 21

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A certain set of test scores has an average (arithmetic mean) of 70 an  [#permalink]

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10 Oct 2016, 02:06
1
1
Given, mean = 70, SD = 25

Mean + 2SD = 120
Mean - 2SD = 20

It has been told that m,n are both in this range.

m,n > 20
m=n=21
Average of 2 numbers is 21(Option E)
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Joined: 17 Nov 2014
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Location: India
Re: A certain set of test scores has an average (arithmetic mean) of 70 an  [#permalink]

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10 Oct 2016, 20:57
1
Given, mean = 70, SD = 25

Mean + 2(Standrad Deviation) = 120
Mean - 2(Standrad Deviation) = 20

m,n are both in this range i.e (20 to 120)
The least value that m,n take is 21 since m,n > 20
m=n=21
Average of 2 numbers is 21

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Joined: 24 Dec 2016
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Re: A certain set of test scores has an average (arithmetic mean) of 70 an  [#permalink]

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19 Feb 2017, 12:05
Bunuel wrote:
A certain set of test scores has an average (arithmetic mean) of 70 and a standard deviation of 25. If m and n, two numbers in the set, are both within 2 standard deviations from the average, then which of the following could be the average of m and n?

A. 10
B. 14
C. 17
D. 19
E. 21

Both the nos. lie between 20 and 120.
The average has to be greater than the lowest no. which is only satisfied by option E.
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Joined: 07 Jun 2017
Posts: 100
Re: A certain set of test scores has an average (arithmetic mean) of 70 an  [#permalink]

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05 Sep 2017, 01:06
I don't have a formula,
M and N won't be smaller than 20
so 21 is the only correct answer.
Re: A certain set of test scores has an average (arithmetic mean) of 70 an   [#permalink] 05 Sep 2017, 01:06
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# A certain set of test scores has an average (arithmetic mean) of 70 an

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