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

It is currently 06 Jul 2020, 01:18

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

In a certain set of numbers, 12.5 is 1.5 units of standard deviation

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

Hide Tags

Find Similar Topics 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 64962
In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 28 Jan 2019, 01:28
1
6
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

68% (02:01) correct 32% (02:07) wrong based on 148 sessions

HideShow timer Statistics

GMAT Club Legend
GMAT Club Legend
User avatar
V
Joined: 18 Aug 2017
Posts: 6425
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
GMAT ToolKit User Reviews Badge CAT Tests
Re: In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 28 Jan 2019, 03:02
3
Bunuel wrote:
In a certain set of numbers, 12.5 is 1.5 units of standard deviation above the mean, and 8.9 is 0.5 units of standard deviation below the mean. What is the mean of the set?

A. 8.9
B. 9.1
C. 9.5
D. 9.8
E. 12.5



given
12.5= M+1.5SD
8.9=M-0.5SD
solve for M
we get
M= 9.8
IMO D
Intern
Intern
avatar
B
Joined: 30 Jul 2018
Posts: 11
GMAT ToolKit User
Re: In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 22 Feb 2020, 17:57
Archit3110 wrote:
Bunuel wrote:
In a certain set of numbers, 12.5 is 1.5 units of standard deviation above the mean, and 8.9 is 0.5 units of standard deviation below the mean. What is the mean of the set?

A. 8.9
B. 9.1
C. 9.5
D. 9.8
E. 12.5



given
12.5= M+1.5SD
8.9=M-0.5SD
solve for M
we get
M= 9.8
IMO D


Can you please explain the operation?

12.5= M+1.5SD —> M = 11
8.9=M-0.5SD —> M = 9.4

We have 2 values for M and none is 9.8

If mix both ecuations:
12.5 + 8.9 = 2M + 1SD —> M = (21.4 - 1SD) / 2. If SD = 1 then M = 10.2

The answer still far from 9.8

Can you please kindly explain me what is wrong in my reasoning?

I solve it in a more subjective way. The mean has to be between 9.4 and 11 because 12.5 - 1.5 = 11 and 8.9 + 0.5 = 9.4. With that in mind only C and D can be the answer, C is to close to the minimum value of the range, so it has to be D.

Is this intuition is right?

But I still do not know how to find the answer with a straightforward math.

Posted from my mobile device
Manhattan Prep Instructor
avatar
Joined: 17 Jul 2019
Posts: 5
GMAT 1: 780 Q51 V45
GMAT 2: 780 Q50 V47
GMAT 3: 770 Q50 V45
Re: In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 22 Feb 2020, 18:29
3
1
From the prompt we can infer that the mean is thrice as close to 8.9 as it is to 12.5. That’s a ratio of 3:1 for a total of 4 ratio units. Take the total distance there (12.5 - 8.9) 3.6, split it four ways and there’s your answer: one ratio unit (0.9) to the right of 8.9.

Posted from my mobile device
Manager
Manager
avatar
G
Joined: 01 Nov 2017
Posts: 106
Location: India
Concentration: Finance, Leadership
Schools: ISB '21
GMAT 1: 690 Q49 V36
GPA: 4
WE: Web Development (Consulting)
GMAT ToolKit User Premium Member
Re: In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 28 Mar 2020, 02:21
1
1
Andresmadeddie

12.5= M+1.5SD —> M = 11
8.9=M-0.5SD —> M = 9.4

You have considered SD value to be 1 which is not correct. 1.5SD is actually (1.5 x Standard deviation value), where Standard deviation value is unknown.

Hence, there are two variables (M & SD) and two equations. We can solve them to find M, like below:

M +(1.5 x SD) = 12.5
M - (0.5 x SD) = 8.9
--------------------------
This will give you M = 9.8 or SD = 1.8. Hence answer is Mean = 9.8, option D.

I hope this helps :)
Intern
Intern
avatar
B
Joined: 30 Jul 2018
Posts: 11
GMAT ToolKit User
Re: In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 28 Mar 2020, 08:37
Thank you! I got a “yeyo time” now seems so obvious that I feel ashamed .
It helps. Thank you!

“Yeyo time” = the brain is So burned that obvious things do not looks obvious at all.

Posted from my mobile device
Manager
Manager
User avatar
G
Joined: 24 Feb 2020
Posts: 165
Location: Italy
WE: Analyst (Investment Banking)
Re: In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 28 Mar 2020, 23:26
My solution:

8.9.........0,5........mean..........1,5.........12.5

Ratio is 1:3 (0,5:1,5)
Total distance = 12.5 - 8.9 = 3.6
3.6 / 4 = 0.9
It means that 0.5 distance = 0.9

Mean = 8.9 + 0.9 = 9.8 | 12.5 - (0,9*3)= 12.5 - 2.7 = 9.8

9.8 is the answer

Bunuel
Intern
Intern
avatar
B
Joined: 13 Dec 2018
Posts: 31
In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 29 Mar 2020, 03:00
Hi Bunuel

Can we write 1.5SD as 1SD + 0.5SD ?

If yes, then by this approach we are getting wrong answer.

Please help.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 64962
Re: In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 29 Mar 2020, 03:04
Intern
Intern
avatar
B
Joined: 13 Dec 2018
Posts: 31
Re: In a certain set of numbers, 12.5 is 1.5 units of standard deviation  [#permalink]

Show Tags

New post 29 Mar 2020, 03:15
Bunuel wrote:
a12bansal wrote:
Hi Bunuel

Can we write 1.5SD as 1SD + 0.5SD ?

If yes, then by this approach we are getting wrong answer.

Please help.


The standard deviation is some number, so naturally, 1.5 SD = 1 SD + 0.5 SD but how are you getting different answer from this?



Sorry Bunuel,

I did some wrong calculation.

Thanks a lot for your prompt reply.
GMAT Club Bot
Re: In a certain set of numbers, 12.5 is 1.5 units of standard deviation   [#permalink] 29 Mar 2020, 03:15

In a certain set of numbers, 12.5 is 1.5 units of standard deviation

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





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