Find all School-related info fast with the new School-Specific MBA Forum

It is currently 25 Aug 2016, 06:53
GMAT Club Tests

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

During an experiment, some water was removed from each of 6

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

Hide Tags

2 KUDOS received
Manager
Manager
avatar
Joined: 12 Apr 2007
Posts: 170
Followers: 1

Kudos [?]: 9 [2] , given: 0

During an experiment, some water was removed from each of 6 [#permalink]

Show Tags

New post 07 Jul 2007, 17:27
2
This post received
KUDOS
6
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

69% (01:38) correct 31% (00:53) wrong based on 188 sessions

HideShow timer Statistics

During an experiment, some water was removed from each of the 6 water tanks. If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?

(1) For each tank, 30% of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.

(2) The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.

OPEN DISCUSSION OF THIS QUESTION IS HERE: during-an-experiment-some-water-was-removed-from-each-of-94166.html
[Reveal] Spoiler: OA

Last edited by Bunuel on 11 May 2014, 06:20, edited 1 time in total.
Renamed the topic, edited the question and added the OA.
1 KUDOS received
Director
Director
avatar
Joined: 12 Jun 2006
Posts: 532
Followers: 2

Kudos [?]: 101 [1] , given: 1

Re: gmatprep standard deviation DS [#permalink]

Show Tags

New post 08 Jul 2007, 03:41
1
This post received
KUDOS
plaguerabbit wrote:
During an experiment, some water was removed from each of 6 water tanks. If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?

(1) For each tank, 30 percent of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.

(2) The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.

OA later
A. since .3 is being removed from each tank won't SD remain the same?
Manager
Manager
avatar
Joined: 12 Apr 2007
Posts: 170
Followers: 1

Kudos [?]: 9 [0], given: 0

Re: gmatprep standard deviation DS [#permalink]

Show Tags

New post 08 Jul 2007, 06:12
ggarr wrote:
plaguerabbit wrote:
During an experiment, some water was removed from each of 6 water tanks. If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?

(1) For each tank, 30 percent of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.

(2) The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.

OA later
A. since .3 is being removed from each tank won't SD remain the same?


no, the concept that i missed here was that the standard deviation would decrease by .3 since the distances between the values were all decreased by 30%.

So the std dev will be 7 from S1
Manager
Manager
avatar
Joined: 15 Nov 2007
Posts: 135
Followers: 1

Kudos [?]: 46 [0], given: 2

Re: gmatprep standard deviation DS [#permalink]

Show Tags

New post 02 May 2008, 00:19
more detailed explanation please
2 KUDOS received
SVP
SVP
avatar
Joined: 04 May 2006
Posts: 1926
Schools: CBS, Kellogg
Followers: 21

Kudos [?]: 855 [2] , given: 1

Premium Member
Re: gmatprep standard deviation DS [#permalink]

Show Tags

New post 02 May 2008, 01:06
2
This post received
KUDOS
dominion wrote:
more detailed explanation please


I think the holder went to the B-school already! :lol:

My computer doesnot support the supericacl, I must write it in a very detail, i explain A only

A.
Beginning:
6 water tanks: t1, t2, t3, t4....t6
mean t =(t1+t2+t3+...+t6)/6
SD =10 = √∑(ti - t)^2 (i = 1...6)

After removing each tanhk 30% water:

6 water tanks: 0.7*t1,.....0.7*t6
new mean =(0.7*t1 + 0.7*t2 +....+0.7*t6)/6 = 0.7* t
new SD = √∑(0.7*ti - 0.7*t)^2 (i = 1...6)
new SD = 0.7*10 =7
_________________

GMAT Club Premium Membership - big benefits and savings

3 KUDOS received
Director
Director
User avatar
Joined: 14 Jan 2007
Posts: 777
Followers: 2

Kudos [?]: 125 [3] , given: 0

Re: gmatprep standard deviation DS [#permalink]

Show Tags

New post 03 May 2008, 11:09
3
This post received
KUDOS
1
This post was
BOOKMARKED
Two important properties of std dev:
1. Adding a constant to each term does not alter the std dev
2. Multiplying each term by a constant leads to the new std dev = constant * old std dev

Property 2 applies here.
1 KUDOS received
GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 09 Sep 2013
Posts: 11050
Followers: 511

Kudos [?]: 134 [1] , given: 0

Premium Member
Re: During an experiment, some water was removed from each of 6 [#permalink]

Show Tags

New post 11 May 2014, 05:19
1
This post received
KUDOS
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.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Expert Post
6 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 34432
Followers: 6255

Kudos [?]: 79450 [6] , given: 10016

Re: During an experiment, some water was removed from each of 6 [#permalink]

Show Tags

New post 11 May 2014, 06:22
6
This post received
KUDOS
Expert's post
2
This post was
BOOKMARKED
During an experiment, some water was removed from each of the 6 water tanks. If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?

(1) For each tank, 30% of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.
(2) The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.

You should know that:
If we add or subtract a constant to each term in a set:
Mean will increase or decrease by the same constant.
SD will not change.

If we increase or decrease each term in a set by the same percent (multiply all terms by the constant):
Mean will increase or decrease by the same percent.
SD will increase or decrease by the same percent.

You can check it yourself:
SD of a set: {1,1,4} will be the same as that of {5,5,8} as second set is obtained by adding 4 to each term of the first set.

That's because Standard Deviation shows how much variation there is from the mean. And when adding or subtracting a constant to each term we are shifting the mean of the set by this constant (mean will increase or decrease by the same constant) but the variation from the mean remains the same as all terms are also shifted by the same constant.

So according to this rules statement (1) is sufficient to get new SD, it'll be 30% less than the old SD so 7. As for statement (2) it's clearly insufficient as knowing mean gives us no help in getting new SD.

Answer: A.

For more on this check Standard Deviation chapter of Math Book: math-standard-deviation-87905.html

Collection of PS questions on SD: ps-questions-about-standard-deviation-85897.html
Collection of PS questions on SD: ds-questions-about-standard-deviation-85896.html

Hope it's clear.

OPEN DISCUSSION OF THIS QUESTION IS HERE: during-an-experiment-some-water-was-removed-from-each-of-94166.html
_________________

New to the Math Forum?
Please read this: All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Re: During an experiment, some water was removed from each of 6   [#permalink] 11 May 2014, 06:22
    Similar topics Author Replies Last post
Similar
Topics:
17 Experts publish their posts in the topic Is the positive integer x divisible by each integer from 2 through 6 ? pego2008 8 14 May 2016, 03:14
16 Experts publish their posts in the topic A certain number of marbles are to be removed from a box con chetan86 4 31 Jul 2014, 21:48
9 Experts publish their posts in the topic Three dice, each with faces numbered from 1 through 6, were fozzzy 8 06 Jul 2013, 02:39
80 Experts publish their posts in the topic During an experiment, some water was removed from each of vaivish1723 19 13 May 2010, 04:07
10 Julian bought 6 kilograms of cheese from each of Deli A and salr15 11 24 Jun 2007, 20:46
Display posts from previous: Sort by

During an experiment, some water was removed from each of 6

  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 and phpBB SEO

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®.