It is currently 23 Jan 2018, 06:02

### 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 June
Open Detailed Calendar

# 46, 47, 48, 49, 50, 51, 52, 53, 54 The standard deviation of the 9 nu

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 4715
GPA: 3.82
46, 47, 48, 49, 50, 51, 52, 53, 54 The standard deviation of the 9 nu [#permalink]

### Show Tags

17 Dec 2017, 23:31
Expert's post
1
This post was
BOOKMARKED
00:00

Difficulty:

35% (medium)

Question Stats:

64% (00:55) correct 36% (01:23) wrong based on 47 sessions

### HideShow timer Statistics

[GMAT math practice question]

$$46, 47, 48, 49, 50, 51, 52, 53, 54$$
The standard deviation of the $$9$$ numbers in the above list lies between $$2$$ and $$3$$. How many of the $$9$$ numbers are within one standard deviation of the average (arithmetic mean)?

A. $$5$$
B. $$6$$
C. $$7$$
D. $$8$$
E. $$9$$
[Reveal] Spoiler: OA

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
Find a 10% off coupon code for GMAT Club members.
“Receive 5 Math Questions & Solutions Daily”
Unlimited Access to over 120 free video lessons - try it yourself

Intern
Joined: 27 Mar 2016
Posts: 13
Location: India
Schools: IIM (S)
GMAT 1: 590 Q49 V21
GPA: 3.9
Re: 46, 47, 48, 49, 50, 51, 52, 53, 54 The standard deviation of the 9 nu [#permalink]

### Show Tags

18 Dec 2017, 06:35
Although I have marked the correct answer, I just want to confirm my approach.

I have calculated s.d of the series 48,49, 50,51,52 (sqrt2.5) and 47,48,49,50,51,52,53(sqrt7)

Please correct me whether my approach is correct.
PS Forum Moderator
Joined: 25 Feb 2013
Posts: 836
Location: India
GPA: 3.82
46, 47, 48, 49, 50, 51, 52, 53, 54 The standard deviation of the 9 nu [#permalink]

### Show Tags

18 Dec 2017, 09:12
MathRevolution wrote:
[GMAT math practice question]

$$46, 47, 48, 49, 50, 51, 52, 53, 54$$
The standard deviation of the $$9$$ numbers in the above list lies between $$2$$ and $$3$$. How many of the $$9$$ numbers are within one standard deviation of the average (arithmetic mean)?

A. $$5$$
B. $$6$$
C. $$7$$
D. $$8$$
E. $$9$$

The mean of the above set is the middle value $$= 50$$

$$2<SD<3$$, as $$1 SD = 1*SD$$

so one $$SD$$ will also be between $$2$$ and $$3$$. SD will be $$2.nnn$$ (2.something). for the sake of calculation let $$SD = 2.5$$

lower limit: $$Mean - S.D = 50 - 2.5 = 47.5$$

upper limit: $$Mean + S.D = 50 + 2.5 = 52.5$$

So numbers lying within 1 $$SD$$ will range from $$48$$ to $$52$$ which are 48, 49, 50, 51 & 52 $$=5$$

Option A
PS Forum Moderator
Joined: 25 Feb 2013
Posts: 836
Location: India
GPA: 3.82
Re: 46, 47, 48, 49, 50, 51, 52, 53, 54 The standard deviation of the 9 nu [#permalink]

### Show Tags

18 Dec 2017, 09:14
ushasi wrote:
Although I have marked the correct answer, I just want to confirm my approach.

I have calculated s.d of the series 48,49, 50,51,52 (sqrt2.5) and 47,48,49,50,51,52,53(sqrt7)

Please correct me whether my approach is correct.

Hi ushasi

Could not get your approach. Can you explain your reason for calculating SD for two different sets as mentioned by you?
Intern
Joined: 10 Dec 2017
Posts: 3
Re: 46, 47, 48, 49, 50, 51, 52, 53, 54 The standard deviation of the 9 nu [#permalink]

### Show Tags

18 Dec 2017, 10:25
MathRevolution wrote:
[GMAT math practice question]

$$46, 47, 48, 49, 50, 51, 52, 53, 54$$
The standard deviation of the $$9$$ numbers in the above list lies between $$2$$ and $$3$$. How many of the $$9$$ numbers are within one standard deviation of the average (arithmetic mean)?

A. $$5$$
B. $$6$$
C. $$7$$
D. $$8$$
E. $$9$$

Solution:
1.The standard deviation of 9 numbers lies between 2 and 3
2. considering standard deviation 2.5 approx. .
3. Mean of the above 9 numbers is 50.
4.Hence numbers lying between Mean + (1 Standard deviation ) = 52.5 and Mean - (1 Standard deviation) = 47.5 are 48,49,50,51 and 52
5. Hence 5 numbers are lying within 1 standard deviation from the Mean. Hence answer is A
_________________

Regards,
Sneha Tatavarthy
Math Facilitator
International Baccalaureate

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 4715
GPA: 3.82
Re: 46, 47, 48, 49, 50, 51, 52, 53, 54 The standard deviation of the 9 nu [#permalink]

### Show Tags

20 Dec 2017, 01:00
=>
The average of the $$9$$ numbers is $$50$$. So, if n lies within one standard deviation of the mean, then
$$50 – 2.xxx < n < 50 + 2.xxx$$
$$47.xxx < n < 52.xxx$$
and $$n = 48, 49, 50, 51, or 52.$$
There are five numbers in this range.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
Find a 10% off coupon code for GMAT Club members.
“Receive 5 Math Questions & Solutions Daily”
Unlimited Access to over 120 free video lessons - try it yourself

Re: 46, 47, 48, 49, 50, 51, 52, 53, 54 The standard deviation of the 9 nu   [#permalink] 20 Dec 2017, 01:00
Display posts from previous: Sort by