GMAT Changed on April 16th - Read about the latest changes here

 It is currently 26 Apr 2018, 17:45

### 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: 5288
GMAT 1: 800 Q59 V59
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, 00:31
Expert's post
1
This post was
BOOKMARKED
00:00

Difficulty:

35% (medium)

Question Stats:

63% (00:55) correct 37% (01:19) wrong based on 59 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.
"Only $79 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Intern Joined: 27 Mar 2016 Posts: 15 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, 07:35 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: 1062 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, 10:12 1 This post was BOOKMARKED 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: 1062 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, 10:14 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, 11:25 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: 5288 GMAT 1: 800 Q59 V59 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, 02:00 => 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. Therefore, the answer is A. Answer : A _________________ 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. "Only$79 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"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, 02:00
Display posts from previous: Sort by