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# The list shown consist of the times, in seconds, that it

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Intern
Joined: 21 Mar 2007
Posts: 35
The list shown consist of the times, in seconds, that it  [#permalink]

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21 Aug 2007, 16:27
3
15
00:00

Difficulty:

65% (hard)

Question Stats:

58% (01:59) correct 42% (02:29) wrong based on 577 sessions

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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
Math Expert
Joined: 02 Sep 2009
Posts: 61549
Re: 70,75, 80,85,90,105,105,130,130,130 The list consists of  [#permalink]

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20 Jan 2012, 01:52
2
5
ruturajp wrote:
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

70 75 80 85 90 105 105 130 130 130

The list shown consist of the times, in seconds, that it took each of 10 school children to run a distance of 400 meter. If the SD of ten running times is 22.4 seconds, rounded to nearest tenth of second, how many of the 10 running times are more than one SD below the mean of the 10 running times?

A. one
B. two
C. three
D. four
E. five

"How many of the 10 running times are more than one SD below the mean" means how many data points from given 10 are less than mean-1SD.

We are given that SD=22.4, so we should find mean --> mean=100 --> there are only 2 data points below 100-22.4=77.6, namely 70 and 75.

Also discussed here: 70-75-80-85-90-105-105-130-130-130-the-list-shown-consist-of-100361.html

Similar problems:
math-questions-mean-score-88502.html?hilit=below%20mean%20deviation
statistics-question-99221.html?hilit=below%20mean%20deviation#p764887

Hope it helps.
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Director
Joined: 10 Jun 2007
Posts: 987
Re: PS- Standard Deviations  [#permalink]

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21 Aug 2007, 16:39
1
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: 172

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Updated on: 21 Aug 2007, 17:50
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, 17:46.
Last edited by Whatever on 21 Aug 2007, 17:50, edited 1 time in total.
Director
Joined: 10 Jun 2007
Posts: 987

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21 Aug 2007, 17:47
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: 34
Re: 70,75, 80,85,90,105,105,130,130,130 The list consists of  [#permalink]

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20 Jan 2012, 00:02
1
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: 104
GPA: 3.72
Re: The list shown consist of the times, in seconds, that it  [#permalink]

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14 Sep 2017, 05:45
1
Tricky Language of the question stem that distracted me to the wrong answer.
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Re: The list shown consist of the times, in seconds, that it  [#permalink]

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16 Sep 2017, 06:32
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.

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Manager
Joined: 16 Jan 2018
Posts: 58
Concentration: Finance, Technology
GMAT 1: 600 Q40 V33
Re: The list shown consist of the times, in seconds, that it  [#permalink]

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10 Jun 2018, 17:20
2
UGH!! The language - " below the mean of 1 SD"
Intern
Joined: 03 Dec 2018
Posts: 7
Re: The list shown consist of the times, in seconds, that it  [#permalink]

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06 Dec 2018, 02:41
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

how many values are more than 1 sd below the mean.
i assumed we need to find the numbers more than (M-1*SD)
Manager
Joined: 14 Jun 2018
Posts: 206
Re: The list shown consist of the times, in seconds, that it  [#permalink]

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06 Dec 2018, 06:03
If the options had 8 as a choice, i would've definitely picked that one.
Manager
Joined: 22 Jan 2018
Posts: 50
Re: The list shown consist of the times, in seconds, that it  [#permalink]

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27 Jan 2019, 23:12
Whatever wrote:
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.

It appears that St. deviation is from the mean and not the median.

Also, the question mentions clearly that we need to consider St. deviation below the mean.
Intern
Joined: 07 Jun 2018
Posts: 2
Re: The list shown consist of the times, in seconds, that it  [#permalink]

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27 Jan 2019, 23:34
Mean = 100. Std = 22.4. Hence, (Mean - 1 Std.) = 100 - 22.4 = 77.6.

Since 70 and 75 are lower than 77.6. A total of two numbers are below one standard deviation of the mean. B.

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Re: The list shown consist of the times, in seconds, that it   [#permalink] 27 Jan 2019, 23:34
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# The list shown consist of the times, in seconds, that it

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