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15 Aug 2016, 04:02
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
84% (00:49) correct
16%
(01:11)
wrong
based on 179
sessions
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A set has an average (arithmetic mean) of 42 and a standard deviation of 1.8. Which of the following values is two standard deviations away from the mean?
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
Updated on: 22 Jan 2020, 17:23
Originally posted by BrentGMATPrepNow on 15 Aug 2016, 07:24.
Last edited by BrentGMATPrepNow on 22 Jan 2020, 17:23, edited 1 time in total.
Last edited by BrentGMATPrepNow on 22 Jan 2020, 17:23, edited 1 time in total.
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Bunuel
A set has an average (arithmetic mean) of 42 and a standard deviation of 1.8. Which of the following values is two standard deviations away from the mean?
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
A little extra background on standard deviations above and below the mean
If, for example, a set has a standard deviation of 4, then:
1 standard deviation = 4
2 standard deviations = 8
3 standard deviations = 12
1.5 standard deviations = 6
0.25 standard deviations = 1
etc
So, if the mean of a set is 9, and the standard deviation is 4, then:
2 standard deviations ABOVE the mean = 17 [since 9 + 2(4) = 17]
1.5 standard deviations BELOW the mean = 3 [since 9 - 1.5(4) = 3]
3 standard deviations ABOVE the mean = 21 [since 9 + 3(4) = 21]
etc.
-----------------------------
For this question, if the standard deviation is 1.8, then two standard deviations = (2)(1.8) = 3.6
So, two standard deviations BELOW the mean = 42 - 3.6 = 38.4
And two standard deviations ABOVE the mean = 42 + 3.6 = 45.6
This means there are two correct answers.
Now check the answer choices for one of the two possible answers.
Answer:
General Discussion
15 Aug 2016, 05:06
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Bunuel
A set has an average (arithmetic mean) of 42 and a standard deviation of 1.8. Which of the following values is two standard deviations away from the mean?
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
AM is 42 and SD is 1.8...
Now, we need to count all numbers greater than 42+2(1.8) = 45.6 or 42-2(1.8) = 38.4 (we are asked to find the value that is two SD away from the mean..so multiply the SD by 2)
Only B is in the list..
IMO option B is correct answer..
OA please...will correct if I missed anything..
