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16 Jul 2018, 01:05
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
55%
(hard)
Question Stats:
65% (01:57) correct
35%
(02:14)
wrong
based on 338
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[GMAT math practice question]
A certain characteristic in a large population has a distribution that is symmetric about the mean m. 68 percent of the distribution lies within one standard deviation d of the mean. The average score of students in a certain class is 72 pts. 84% of students in the class score less than 80 pts. What is the standard deviation of the students’ scores?
A. 1
B. 2
C. 4
D. 8
E. 16
A certain characteristic in a large population has a distribution that is symmetric about the mean m. 68 percent of the distribution lies within one standard deviation d of the mean. The average score of students in a certain class is 72 pts. 84% of students in the class score less than 80 pts. What is the standard deviation of the students’ scores?
A. 1
B. 2
C. 4
D. 8
E. 16
16 Jul 2018, 04:17
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MathRevolution
Given, 84% of students in the class score less than 80 pts.
In the standard normal distribution curve, region of 84% students lies to the left of (m+d), where m=mean, d=standard deviation.
Given, m=72, we have m+d=80
Or, 72+d=80
or, d=80-72=8
Ans. (D)
18 Jul 2018, 05:03
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Attachment:
7.18.png [ 27.93 KiB | Viewed 5370 times ]
80 – 72 = 8 is the standard deviation of the distribution.
Therefore, D is the answer.
Answer: D
