GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 22 Jan 2019, 19:20

### 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

## Events & Promotions

###### Events & Promotions in January
PrevNext
SuMoTuWeThFrSa
303112345
6789101112
13141516171819
20212223242526
272829303112
Open Detailed Calendar
• ### The winners of the GMAT game show

January 22, 2019

January 22, 2019

10:00 PM PST

11:00 PM PST

In case you didn’t notice, we recently held the 1st ever GMAT game show and it was awesome! See who won a full GMAT course, and register to the next one.
• ### Key Strategies to Master GMAT SC

January 26, 2019

January 26, 2019

07:00 AM PST

09:00 AM PST

Attend this webinar to learn how to leverage Meaning and Logic to solve the most challenging Sentence Correction Questions.

# Teachers in United States high schools teach an average (arithmetic me

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 52390
Teachers in United States high schools teach an average (arithmetic me  [#permalink]

### Show Tags

29 Nov 2016, 00:19
00:00

Difficulty:

15% (low)

Question Stats:

81% (01:09) correct 19% (01:27) wrong based on 77 sessions

### HideShow timer Statistics

Teachers in United States high schools teach an average (arithmetic mean) of 80 hours per month, with a variance of 100. which of the following numbers of monthly teaching hours is exactly two standard deviations away from the mean?

A. 60
B. 75
C. 78
D. 82
E. 90

_________________
Intern
Joined: 01 Feb 2014
Posts: 4
Re: Teachers in United States high schools teach an average (arithmetic me  [#permalink]

### Show Tags

29 Nov 2016, 00:41
1
Bunuel wrote:
Teachers in United States high schools teach an average (arithmetic mean) of 80 hours per month, with a variance of 100. which of the following numbers of monthly teaching hours is exactly two standard deviations away from the mean?

A. 60
B. 75
C. 78
D. 82
E. 90

Standard Dev = sqrt(100) = 10
2 times SD = 20
Away from mean 80 can be either (80+20) or (80-20) = 60 or 100

Ans A)
Target Test Prep Representative
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2830
Re: Teachers in United States high schools teach an average (arithmetic me  [#permalink]

### Show Tags

02 Dec 2016, 09:43
1
Bunuel wrote:
Teachers in United States high schools teach an average (arithmetic mean) of 80 hours per month, with a variance of 100. which of the following numbers of monthly teaching hours is exactly two standard deviations away from the mean?

A. 60
B. 75
C. 78
D. 82
E. 90

We are given that teachers in United States high schools teach an average (arithmetic mean) of 80 hours per month, with a variance of 100. We need to determine which answer choice is two standard deviations from the mean.

Recall that the standard deviation is equal to the square root of the variance.

Since the variance is 100, the standard deviation is √100 = 10, and thus two standard deviations is 10 x 2 = 20. Two standard deviations above the mean yields 80 + 20 = 100. Two standard deviations below the mean is 80 - 20 = 60. Only the value 60 is given as an answer choice.

_________________

Jeffery Miller

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Non-Human User
Joined: 09 Sep 2013
Posts: 9461
Re: Teachers in United States high schools teach an average (arithmetic me  [#permalink]

### Show Tags

15 Apr 2018, 13:44
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: Teachers in United States high schools teach an average (arithmetic me &nbs [#permalink] 15 Apr 2018, 13:44
Display posts from previous: Sort by