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A certain characteristic in a large population has a distribution that

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Math Revolution GMAT Instructor
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A certain characteristic in a large population has a distribution that  [#permalink]

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New post 16 Jul 2018, 00:05
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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

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Re: A certain characteristic in a large population has a distribution that  [#permalink]

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New post 16 Jul 2018, 03:17
1
MathRevolution wrote:
[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


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)
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Re: A certain characteristic in a large population has a distribution that  [#permalink]

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New post 18 Jul 2018, 04:03
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80 – 72 = 8 is the standard deviation of the distribution.

Therefore, D is the answer.

Answer: D
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Re: A certain characteristic in a large population has a distribution that  [#permalink]

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New post 29 Jul 2018, 05:11
Bunuel KarishmaB can you please explain me this problem?
I know the logic behind these kinds of problems, but this one requires some additional efforts to solve smoothly. I want to understand the rationale of it. Thank you.
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Re: A certain characteristic in a large population has a distribution that &nbs [#permalink] 29 Jul 2018, 05:11
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