[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
5-Day Free Trial
5-day free, full-access trial TTP
Available with Beat the GMAT members only code
MORE DETAILS
A certain characteristic in a large population has a distrib
This topic has expert replies
-
Max@Math Revolution
- Elite Legendary Member
- Posts: 3991
- Joined: Fri Jul 24, 2015 2:28 am
- Location: Las Vegas, USA
- Thanked: 19 times
- Followed by:37 members
Timer
00:00
Your Answer
A
B
C
D
E
Global Stats
Math Revolution
The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online.
Email to : [email protected]
Given, 84% of the 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.
Regards!
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.
Regards!
-
Max@Math Revolution
- Elite Legendary Member
- Posts: 3991
- Joined: Fri Jul 24, 2015 2:28 am
- Location: Las Vegas, USA
- Thanked: 19 times
- Followed by:37 members
80 - 72 = 8 is the standard deviation of the distribution.
Therefore, D is the answer.
Answer: D
Math Revolution
The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online.
Email to : [email protected]
GMAT/MBA Expert
-
Scott@TargetTestPrep
- GMAT Instructor
- Posts: 7245
- Joined: Sat Apr 25, 2015 10:56 am
- Location: Los Angeles, CA
- Thanked: 43 times
- Followed by:29 members
Since the distribution is symmetric, 50 percent of the data points in the distribution are less than m and 68/2 = 34 percent of the data points in the distribution are between m and m + d. Therefore, a total of 50 + 34 = 84 percent of the data points in the distribution are less than m + d.Max@Math Revolution wrote: ↑Sun Jul 15, 2018 11:58 pm[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
Answer: D
Scott Woodbury-Stewart
Founder and CEO
[email protected]
See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews
