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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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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 V
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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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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##### General Discussion
Director  Joined: 10 Jun 2007
Posts: 987

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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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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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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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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  B
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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1
Tricky Language of the question stem that distracted me to the wrong answer.
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Target Test Prep Representative G
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2801
Re: The list shown consist of the times, in seconds, that it  [#permalink]

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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  B
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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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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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  G
Joined: 14 Jun 2018
Posts: 206
Re: The list shown consist of the times, in seconds, that it  [#permalink]

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

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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  B
Joined: 07 Jun 2018
Posts: 2
Re: The list shown consist of the times, in seconds, that it  [#permalink]

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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.

Enviado desde mi iPhone utilizando GMAT Club Forum Re: The list shown consist of the times, in seconds, that it   [#permalink] 27 Jan 2019, 23:34
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