GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

 It is currently 25 Jan 2020, 09:56 ### 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

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.  # The list shown consists of the times, in seconds, that it took each of

Author Message
TAGS:

### Hide Tags

Manager  Joined: 13 Aug 2009
Posts: 107
WE 1: 4 years in IT
The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

3
16 00:00

Difficulty:   55% (hard)

Question Stats: 64% (02:07) correct 36% (02:16) wrong based on 553 sessions

### HideShow timer Statistics

70, 75, 80, 85, 90, 105, 105, 130, 130, 130

The list shown consists of the times, in seconds, that it took each of 10 schoolchildren to run a distance of 400 on of meters. If the standard devastation of the 10 running times is 22.4 seconds, 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. one
B. two
C. three
D. four
E. five

Originally posted by raghavs on 28 Mar 2010, 10:42.
Last edited by Bunuel on 15 Oct 2019, 06:51, edited 4 times in total.
Math Expert V
Joined: 02 Sep 2009
Posts: 60647
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

2
6
karthiksms wrote:
Could someone please explain this? thanks

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.
_________________
##### General Discussion
Manager  Joined: 30 Aug 2009
Posts: 216
Location: India
Concentration: General Management
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

1
raghavs wrote:
standard deviation..first question stumped me

OA--TWO

the mean of the 10 running times is 100 sec. we need to find how many of the recorded times are less than 1 SD below the mean i.e how many took less than 100 sec - 1SD = 100 sec - 22.4 sec = 77.6sec. The times are 70 and 75. hence 2
Manager  Joined: 01 Feb 2010
Posts: 171
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

raghavs wrote:
standard deviation..first question stumped me

OA--TWO

mean is 99
SD is 22.4
One SD block away = 99-22.4 = 76.6
so there are two numbers less than mean which are One SD block away 70 & 75 hence TWO.
Manager  Status: D-Day is on February 10th. and I am not stressed
Affiliations: American Management association, American Association of financial accountants
Joined: 12 Apr 2011
Posts: 154
Location: Kuwait
Schools: Columbia university
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

first add the values and devide by 10 to get the mean of 100.
then butract 22.4 from the 100.....> 100-22.4=76.6

check how many numbers in the list are less than 76.6! there are two numbers

hope this helps
Math Expert V
Joined: 02 Sep 2009
Posts: 60647
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

Bumping for review and further discussion*. Get a kudos point for an alternative solution!

*New project from GMAT Club!!! Check HERE
_________________
Manager  Joined: 27 Apr 2012
Posts: 57
Location: United States
GMAT Date: 06-11-2013
GPA: 3.5
WE: Marketing (Consumer Products)
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

1
The first step here is to calculate the mean :

(70+75+80+85+90+105+105+130+130+130)/10 = 100

SD = 22.4,

one SD below the mean = (100 – 22.4) = 77.6

Only 2 values 70 and 75 are less than 77.6, hence B is the answer
Intern  Joined: 26 Mar 2013
Posts: 11
Location: United States
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

To find the mean, take a wild stab and pick a number within the range provided by the given numbers. Now, find the delta between that number and each number in the set. So now you get the overall delta from your "assumed mean". Split that up equally among each number. So adding that to your "assumed mean" will give you the actual mean.

I took 100 and found the difference between it and each of the numbers in the set. Turns out that the overall delta neatly becomes 0. So 100 is the actual mean.
Manager  Joined: 28 Feb 2012
Posts: 103
GPA: 3.9
WE: Marketing (Other)
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

2
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

The most time consuming part in this question is to define the mean. Under exam pressure and time pressure it is very easy to make mistake.
it is easier to group numbers: 130*3=390; 105*2=210; 75+85=160; 70+80=150; 90;
Next stage combine results, again using more convenient ways to calculate: 390+210=600; 160+150=310; 90. 600+310+90=1000. Since there are 10 numbers the mean is 100. Questions asks to find the quantity of numbers one SD BELOW the mean, which is 100-22,4=77,6. There are only two numbers below 77,6. The answer is B
Manager  Joined: 07 Apr 2012
Posts: 87
Location: United States
Concentration: Entrepreneurship, Operations
Schools: ISB '15
GMAT 1: 590 Q48 V23
GPA: 3.9
WE: Operations (Manufacturing)
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

ziko wrote:
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

The most time consuming part in this question is to define the mean. Under exam pressure and time pressure it is very easy to make mistake.
it is easier to group numbers: 130*3=390; 105*2=210; 75+85=160; 70+80=150; 90;
Next stage combine results, again using more convenient ways to calculate: 390+210=600; 160+150=310; 90. 600+310+90=1000. Since there are 10 numbers the mean is 100. Questions asks to find the quantity of numbers one SD BELOW the mean, which is 100-22,4=77,6. There are only two numbers below 77,6. The answer is B

Pardon me for my understanding, but "are <more than> <one SD below the mean> of the 10 running times?
So isn't it asking values greater than 77.6 ?
Math Expert V
Joined: 02 Sep 2009
Posts: 60647
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

ygdrasil24 wrote:
ziko wrote:
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

The most time consuming part in this question is to define the mean. Under exam pressure and time pressure it is very easy to make mistake.
it is easier to group numbers: 130*3=390; 105*2=210; 75+85=160; 70+80=150; 90;
Next stage combine results, again using more convenient ways to calculate: 390+210=600; 160+150=310; 90. 600+310+90=1000. Since there are 10 numbers the mean is 100. Questions asks to find the quantity of numbers one SD BELOW the mean, which is 100-22,4=77,6. There are only two numbers below 77,6. The answer is B

Pardon me for my understanding, but "are <more than> <one SD below the mean> of the 10 running times?
So isn't it asking values greater than 77.6 ?

How many of the 10 running times are more than one SD below the mean. So more than Mean-SD.

How many of the 10 running times are more than one SD below the mean. So less than Mean-SD.
_________________
Manager  Joined: 07 Apr 2012
Posts: 87
Location: United States
Concentration: Entrepreneurship, Operations
Schools: ISB '15
GMAT 1: 590 Q48 V23
GPA: 3.9
WE: Operations (Manufacturing)
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

Bunuel wrote:
ygdrasil24 wrote:
ziko wrote:
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

The most time consuming part in this question is to define the mean. Under exam pressure and time pressure it is very easy to make mistake.
it is easier to group numbers: 130*3=390; 105*2=210; 75+85=160; 70+80=150; 90;
Next stage combine results, again using more convenient ways to calculate: 390+210=600; 160+150=310; 90. 600+310+90=1000. Since there are 10 numbers the mean is 100. Questions asks to find the quantity of numbers one SD BELOW the mean, which is 100-22,4=77,6. There are only two numbers below 77,6. The answer is B

Pardon me for my understanding, but "are <more than> <one SD below the mean> of the 10 running times?
So isn't it asking values greater than 77.6 ?

How many of the 10 running times are more than one SD below the mean. So more than Mean-SD.

How many of the 10 running times are more than one SD below the mean. So less than Mean-SD.

Why couldnt they have written it as
How many of the 10 running times are less than one SD below the mean. This is frustrating for me Manager  B
Joined: 02 Jun 2016
Posts: 59
Location: United States (MA)
GMAT 1: 770 Q51 V44 GPA: 2.4
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

1
Instead of wasting valuable time adding up all 10 numbers, you can spot some easy clues the GMAT leaves behind. The first 5 numbers are perfectly symmetric around 80, so you know mean of the first 5 is 80. The second half of numbers can be quickly added together- 3*130 = 390 and 105*2 = 210 for a sum of 600. Divide by 5 to get 120. Since the first half has a mean of 80 and second half has a mean of 120, and both halves have equal weight (they both represent 5 integers), the average of both halves will be right in the middle at 100. From there figuring out the answer is business as usual.

Sent from my SM-G928T using GMAT Club Forum mobile app
Target Test Prep Representative V
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 9142
Location: United States (CA)
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

raghavs wrote:
70, 75, 80, 85, 90, 105, 105, 130, 130, 130
The list shown consists of the times, in seconds, that it took each of 10 schoolchildren to run a distance of 400 on of meters. If the standard devastation of the 10 running times is 22.4 seconds, 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. one
B. two
C. three
D. four
E. five

The average (mean) is:

(70 + 75 + 80 + 85 + 90 + 105 + 105 + 130 +130 +130)/10 = 1000/10 = 100

Thus, 1 standard deviation below the mean is 100 - 22.4 = 77.6, so there are 2 running times that are more than 1 standard deviation below the mean.

_________________

# Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com

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.

Non-Human User Joined: 09 Sep 2013
Posts: 14012
Re: The list shown consists of the times, in seconds, that it took each of  [#permalink]

### Show Tags

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________ Re: The list shown consists of the times, in seconds, that it took each of   [#permalink] 03 Dec 2019, 19:12
Display posts from previous: Sort by

# The list shown consists of the times, in seconds, that it took each of  