It is currently 10 Dec 2017, 19:26

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

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If the average (arithmetic mean) of 7 numbers is 21, what is the stand

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

Hide Tags

Expert Post
Math Revolution GMAT Instructor
User avatar
P
Joined: 16 Aug 2015
Posts: 4451

Kudos [?]: 3125 [0], given: 0

GPA: 3.82
Premium Member
If the average (arithmetic mean) of 7 numbers is 21, what is the stand [#permalink]

Show Tags

New post 15 Aug 2017, 01:30
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

64% (00:39) correct 36% (00:30) wrong based on 97 sessions

HideShow timer Statistics

If the average (arithmetic mean) of 7 numbers is 21, what is the standard deviation of the numbers?

1) The smallest number of them is 21
2) The greatest number of them is 21
[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
See our Youtube demo

Kudos [?]: 3125 [0], given: 0

1 KUDOS received
Manager
Manager
User avatar
S
Joined: 05 Dec 2016
Posts: 248

Kudos [?]: 26 [1], given: 49

Concentration: Strategy, Finance
GMAT 1: 620 Q46 V29
GMAT ToolKit User
Re: If the average (arithmetic mean) of 7 numbers is 21, what is the stand [#permalink]

Show Tags

New post 15 Aug 2017, 02:20
1
This post received
KUDOS
(1) If the smallest number is 21, then any other number in the set should be at least 21.
Average number would be equal to 21 only if all the numbers in the set would be equal to 21. Thus it means that SD is zero.
SUFF.
(2) If the highest number is 21, then applying same the same logic as statement 1, any other number in the set should be equal to 21 to make the average equal to 21. If any number would be less, then average will be less than 21. Thus again SD is zero and statement 2 is SUFF.

Answer D.

Kudos [?]: 26 [1], given: 49

Expert Post
Math Revolution GMAT Instructor
User avatar
P
Joined: 16 Aug 2015
Posts: 4451

Kudos [?]: 3125 [0], given: 0

GPA: 3.82
Premium Member
Re: If the average (arithmetic mean) of 7 numbers is 21, what is the stand [#permalink]

Show Tags

New post 17 Aug 2017, 00:51
=>Condition 1)
Since the minimum number and the average are same, all numbers should be 21.

Condition 2)
Since the maximum number and the average are same, all numbers should be 21.

Ans: D
_________________

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
See our Youtube demo

Kudos [?]: 3125 [0], given: 0

Manager
Manager
avatar
S
Joined: 15 Feb 2017
Posts: 74

Kudos [?]: 63 [0], given: 0

Re: If the average (arithmetic mean) of 7 numbers is 21, what is the stand [#permalink]

Show Tags

New post 17 Aug 2017, 00:59
The smallest number is 21. Of the other three numbers if any one is greater than 21 then one of the numbers is less than 21 since the avearge is 21. For eg 19,21,23. If the largest is 21 then all the numbers have to be 21 for the same reason. So the answer is D.

Kudos [?]: 63 [0], given: 0

Re: If the average (arithmetic mean) of 7 numbers is 21, what is the stand   [#permalink] 17 Aug 2017, 00:59
Display posts from previous: Sort by

If the average (arithmetic mean) of 7 numbers is 21, what is the stand

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


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.