The residents of the town x participated in a survey to determine the number of hours per week each resident spent watching television. The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hrs. The number of hrs that pat, a resident, watched television last week was between 1 and 2 standard deviation below the mean. which of the following could be the number of hours that pat watched television last week?
1. 30
2. 18
3. 12
4. 20
5. 6
Can you please explain this?
GMAT PREP QUESTION
This topic has expert replies
- g.shankaran
- Master | Next Rank: 500 Posts
- Posts: 101
- Joined: Tue Oct 27, 2009 8:19 am
- Thanked: 4 times
- Followed by:2 members
- vineeshp
- Legendary Member
- Posts: 965
- Joined: Thu Jan 28, 2010 12:52 am
- Thanked: 156 times
- Followed by:34 members
- GMAT Score:720
The number of hrs that pat, a resident, watched television last week was between 1 and 2 standard deviation below the mean.
Is something missing here?
Is something missing here?
Vineesh,
Just telling you what I know and think. I am not the expert.
Just telling you what I know and think. I am not the expert.
- g.shankaran
- Master | Next Rank: 500 Posts
- Posts: 101
- Joined: Tue Oct 27, 2009 8:19 am
- Thanked: 4 times
- Followed by:2 members
- g.shankaran
- Master | Next Rank: 500 Posts
- Posts: 101
- Joined: Tue Oct 27, 2009 8:19 am
- Thanked: 4 times
- Followed by:2 members
Please correct me if I am wrong.g.shankaran wrote:The residents of the town x participated in a survey to determine the number of hours per week each resident spent watching television. The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hrs. The number of hrs that pat, a resident, watched television last week was between 1 and 2 standard deviation below the mean. which of the following could be the number of hours that pat watched television last week?
1. 30
2. 18
3. 12
4. 20
5. 6
Can you please explain this?
Here the SD is 6 and the mean = 21.
Pat watched television between 1 and 2 SD below mean. So assuming 1.5 SD, which is equal to 1.5 x 6 = 9. here the mean is 21. So the value could be 21-9 = 12.
-
- Newbie | Next Rank: 10 Posts
- Posts: 4
- Joined: Mon Oct 08, 2007 1:23 am
In my view it is given that PAT has seen Television between 1 & 2 SD below mean which means:
As SD= 6 hrs(given)
1 SD= 6 hrs
2 SD= 12 hrs
Therefore its between 6 to 12 hrs below 21(mean)i.e between 9 hrs to 15 hrs
The only available option between 9 and 15 hrs is 12 hrs
Hence 12 is the answer
As SD= 6 hrs(given)
1 SD= 6 hrs
2 SD= 12 hrs
Therefore its between 6 to 12 hrs below 21(mean)i.e between 9 hrs to 15 hrs
The only available option between 9 and 15 hrs is 12 hrs
Hence 12 is the answer
- Stuart@KaplanGMAT
- GMAT Instructor
- Posts: 3225
- Joined: Tue Jan 08, 2008 2:40 pm
- Location: Toronto
- Thanked: 1710 times
- Followed by:614 members
- GMAT Score:800
This question is typical of the most common way the GMAT is currently testing standard deviation. All you need to solve is a very basic understanding of what SD is - the question itself is much simpler than it seems.g.shankaran wrote:The residents of the town x participated in a survey to determine the number of hours per week each resident spent watching television. The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hrs. The number of hrs that pat, a resident, watched television last week was between 1 and 2 standard deviation below the mean. which of the following could be the number of hours that pat watched television last week?
1. 30
2. 18
3. 12
4. 20
5. 6
Can you please explain this?
To solve quickly every time, draw a number line and put the mean in the middle:
------------------21-------------------
Next, see if the question is asking for a number "below", "above" or "within" x standard deviations from the mean.
If "below", only worry about numbers below the mean.
If "above", only worry about numbers above the mean.
If "within", worry about numbers both below and above the mean.
(Questions can also ask about "from the mean", in which case you go below and above.)
This question asks for a number "between 1 and 2 standard deviation below the mean", so we work our way down from 21.
The SD is 6, so count off blocks of 6 to the left of the mean, 21:
-------3---------9----------15-----------21
Each number on the line represents 1 more SD below the mean. In other words:
15 is 1 SD below the mean;
9 is 2 SDs below the mean; and
3 is 3 SDs below the mean.
Since we want a number "between 1 and 2 standard deviation below the mean", any number between 9 and 15 fits the bill: choose (C)12.
If you understand how these questions work, they only take about 15 seconds to solve.
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course