List M (not shown) consists of 8 different integers, each of which is in the list shown below:
4,6,8,10,12,14,16,18,20,22
What is the SD of the numbers in the list M?
1) The average (Arithmetic Mean) of the numbers in the list M is equal to the average of the numbers in the list shown
2) List M does not contain 22
Need help with this DS question!
This topic has expert replies
-
- Senior | Next Rank: 100 Posts
- Posts: 44
- Joined: Tue Mar 05, 2013 10:18 pm
- Thanked: 4 times
-
- Junior | Next Rank: 30 Posts
- Posts: 14
- Joined: Wed Apr 24, 2013 6:14 am
- Location: Global
- Thanked: 8 times
- Followed by:2 members
- GMAT Score:790
The standard deviation is the same as the average OF the average distance from the mean.
To find the standard deviation, we need the mean, and the average distance of all points from the mean. We can certainly get this from having all members of the set, but that is NOT necessary.
1) provides the mean. It DOES NOT provide the distribution of the numbers.
INSUFFICIENT
2) does NOT provide the mean, or the distribution of numbers.
INSUFFICIENT
Putting them together, however, may yield the distribution.
We know from 1) that the mean is 13. Since each number can only appear once, and we need 4 numbers above the mean, we know that 14, 16, 18, and 20 are in the set. To get an average of 13, they must be complemented by 6, 8, 10, 12, so we now have the full set and can compute the Standard Deviation.
So out answer is C.
Note, we don't need to outline the entire set, just get to the point where we REALIZE that we can narrow down to the actual set.
Ben[/i]
To find the standard deviation, we need the mean, and the average distance of all points from the mean. We can certainly get this from having all members of the set, but that is NOT necessary.
1) provides the mean. It DOES NOT provide the distribution of the numbers.
INSUFFICIENT
2) does NOT provide the mean, or the distribution of numbers.
INSUFFICIENT
Putting them together, however, may yield the distribution.
We know from 1) that the mean is 13. Since each number can only appear once, and we need 4 numbers above the mean, we know that 14, 16, 18, and 20 are in the set. To get an average of 13, they must be complemented by 6, 8, 10, 12, so we now have the full set and can compute the Standard Deviation.
So out answer is C.
Note, we don't need to outline the entire set, just get to the point where we REALIZE that we can narrow down to the actual set.
Ben[/i]
-
- Senior | Next Rank: 100 Posts
- Posts: 44
- Joined: Tue Mar 05, 2013 10:18 pm
- Thanked: 4 times
Hi,
Thanks for the solution. I have one doubt though.
Why can each number only appear once and 4 numbers need to be above the mean (13)?
Regards,
Rishi
Thanks for the solution. I have one doubt though.
Why can each number only appear once and 4 numbers need to be above the mean (13)?
Regards,
Rishi
- OfficialGMAT
- Official Company Rep
- Posts: 669
- Joined: Tue Jun 12, 2012 9:06 pm
- Location: Washington DC
- Thanked: 143 times
- Followed by:270 members
- GMAT Score:800
Hi, all! This thread is for questions for the makers of the GMAT exam. Unfortunately we cannot help you with answers to specific practice questions. Please re-post this to one of the main threads. Thank you!
Rebecca
Rebecca
Leah
Official GMAC Representative
Have a question about customer service issues, GMAT exam policies, or GMAT exam structure? Post your question in our Ask the Test Maker forum!
Official GMAC Representative
Have a question about customer service issues, GMAT exam policies, or GMAT exam structure? Post your question in our Ask the Test Maker forum!