Author 
Message 
TAGS:

Hide Tags

Manager
Joined: 21 Mar 2007
Posts: 50

The list shown consist of the times, in seconds, that it
[#permalink]
Show Tags
21 Aug 2007, 17:27
Question Stats:
59% (01:26) correct 41% (01:43) wrong based on 396 sessions
HideShow timer Statistics
70,75, 80,85,90,105,105,130,130,130 The list consists of the times in seconds that it took each of the 10 school children to run a distance of 400 mts . If the standard deviation of the 10 running times is 22.4, rounded to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times. A. 1 B. 2 C. 3 D. 4 E. 5
Official Answer and Stats are available only to registered users. Register/ Login.




Math Expert
Joined: 02 Sep 2009
Posts: 47983

Re: 70,75, 80,85,90,105,105,130,130,130 The list consists of
[#permalink]
Show Tags
20 Jan 2012, 02:52




VP
Joined: 10 Jun 2007
Posts: 1394

Re: PS Standard Deviations
[#permalink]
Show Tags
21 Aug 2007, 17:39
forgmat wrote: 70,75, 80,85,90,105,105,130,130,130
The list consists of the times in seconds that it took each of the 10 school children to run a distance of 400 mts . If the standard deviation of the 10 running times is 22.4, rounded to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times.
a. 1 b.2 c.3 d.4 e.5
I think the key here is to know what "1 standard deviation" means.
1 standard deviation = 1 * 22.4 = 22.4
Now, find the average:
Avg = (70+75+80+85+90+105+105+130+130+130)/10 = 1000/10 = 100
So rage should be 100 +/ 22.4 = 77.6 and 122.4
Looks like E is the answer.



Manager
Joined: 03 Sep 2006
Posts: 232

[#permalink]
Show Tags
Updated on: 21 Aug 2007, 18:50
Got 5 people:
1) Median is (90+105)/2 = 97.5
2) St. deviation: 97.5 +/ 22.4 = 75,1 from the left, and 119,9 from the right.
3) From the left we have 2 child (70 and 75), and from the right  3 child (130, 130 and 130)
Ans. E
P.S> I can't see how the answ. can be 2, if assw. is 2  it logically could be only 70 and 75, but if you add 2 st. dev. = 44.8 to 80, you'll get 124.8  so 3*130 still do not fit in this pattern %)
Originally posted by Whatever on 21 Aug 2007, 18:46.
Last edited by Whatever on 21 Aug 2007, 18:50, edited 1 time in total.



VP
Joined: 10 Jun 2007
Posts: 1394

forgmat wrote: sorry just found a link where this question was posted earlier on gmat club. no the answer is 2
I think I see the point here. Although five people are in the "range", three are above, and two are below. So the answer is 2, I guess that's what the question is asking for.



Intern
Joined: 05 Oct 2011
Posts: 44

Re: 70,75, 80,85,90,105,105,130,130,130 The list consists of
[#permalink]
Show Tags
20 Jan 2012, 01:02
how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times. I din get the question can any1 explain



Manager
Joined: 30 Jul 2014
Posts: 151
GPA: 3.72

Re: The list shown consist of the times, in seconds, that it
[#permalink]
Show Tags
14 Sep 2017, 06:45
Tricky Language of the question stem that distracted me to the wrong answer.
_________________
A lot needs to be learned from all of you.



Target Test Prep Representative
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2727

Re: The list shown consist of the times, in seconds, that it
[#permalink]
Show Tags
16 Sep 2017, 07:32
forgmat wrote: 70,75, 80,85,90,105,105,130,130,130
The list consists of the times in seconds that it took each of the 10 school children to run a distance of 400 mts . If the standard deviation of the 10 running times is 22.4, rounded to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times.
A. 1 B. 2 C. 3 D. 4 E. 5 Let’s calculate the average: (70 + 75 + 80 + 85 + 90 + 105 + 105 + 130 + 130 + 130)/10 = 1000/10 = 100 One standard deviation below the mean is 100  22.4 = 77.6, so there are 2 running times more than 1 standard deviation below the mean. Answer: B
_________________
Jeffery Miller
Head of GMAT Instruction
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



Manager
Joined: 16 Jan 2018
Posts: 58
Concentration: Finance, Technology

Re: The list shown consist of the times, in seconds, that it
[#permalink]
Show Tags
10 Jun 2018, 18:20
UGH!! The language  " below the mean of 1 SD"




Re: The list shown consist of the times, in seconds, that it &nbs
[#permalink]
10 Jun 2018, 18:20






