Summer is Coming! Join the Game of Timers Competition to Win Epic Prizes. Registration is Open. Game starts Mon July 1st.

It is currently 16 Jul 2019, 11:34

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

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

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Find Similar Topics 
Intern
Intern
avatar
Joined: 21 Mar 2007
Posts: 45
The list shown consist of the times, in seconds, that it  [#permalink]

Show Tags

New post 21 Aug 2007, 17:27
3
14
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

58% (02:00) correct 42% (02:30) wrong based on 537 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
Most Helpful Expert Reply
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 56244
Re: 70,75, 80,85,90,105,105,130,130,130 The list consists of  [#permalink]

Show Tags

New post 20 Jan 2012, 02:52
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.

Answer: B.

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.
_________________
General Discussion
VP
VP
avatar
Joined: 10 Jun 2007
Posts: 1298
Re: PS- Standard Deviations  [#permalink]

Show Tags

New post 21 Aug 2007, 17:39
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
Manager
avatar
Joined: 03 Sep 2006
Posts: 223
  [#permalink]

Show Tags

New post 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
VP
avatar
Joined: 10 Jun 2007
Posts: 1298
  [#permalink]

Show Tags

New post 21 Aug 2007, 18:47
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
Intern
avatar
Joined: 05 Oct 2011
Posts: 36
Re: 70,75, 80,85,90,105,105,130,130,130 The list consists of  [#permalink]

Show Tags

New post 20 Jan 2012, 01:02
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
Manager
User avatar
S
Joined: 30 Jul 2014
Posts: 121
GPA: 3.72
Reviews Badge
Re: The list shown consist of the times, in seconds, that it  [#permalink]

Show Tags

New post 14 Sep 2017, 06:45
1
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
User avatar
G
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2823
Re: The list shown consist of the times, in seconds, that it  [#permalink]

Show Tags

New post 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
_________________

Jeffrey Miller

Head of GMAT Instruction

Jeff@TargetTestPrep.com
TTP - Target Test Prep Logo
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Manager
Manager
avatar
B
Joined: 16 Jan 2018
Posts: 62
Concentration: Finance, Technology
GMAT 1: 600 Q40 V33
Reviews Badge
Re: The list shown consist of the times, in seconds, that it  [#permalink]

Show Tags

New post 10 Jun 2018, 18:20
2
UGH!! The language - " below the mean of 1 SD" :fuming
Intern
Intern
avatar
Joined: 03 Dec 2018
Posts: 7
Re: The list shown consist of the times, in seconds, that it  [#permalink]

Show Tags

New post 06 Dec 2018, 03:41
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
Manager
avatar
G
Joined: 14 Jun 2018
Posts: 222
Re: The list shown consist of the times, in seconds, that it  [#permalink]

Show Tags

New post 06 Dec 2018, 07:03
If the options had 8 as a choice, i would've definitely picked that one.
Intern
Intern
avatar
B
Joined: 22 Jan 2018
Posts: 47
Re: The list shown consist of the times, in seconds, that it  [#permalink]

Show Tags

New post 28 Jan 2019, 00:12
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
Intern
avatar
B
Joined: 07 Jun 2018
Posts: 2
Re: The list shown consist of the times, in seconds, that it  [#permalink]

Show Tags

New post 28 Jan 2019, 00:34
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.


Enviado desde mi iPhone utilizando GMAT Club Forum
GMAT Club Bot
Re: The list shown consist of the times, in seconds, that it   [#permalink] 28 Jan 2019, 00:34
Display posts from previous: Sort by

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

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  





Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne