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

It is currently 23 Jul 2014, 02:12

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

PS - Looking for easy calculation trick

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
User avatar
Joined: 17 Dec 2008
Posts: 179
Followers: 1

Kudos [?]: 33 [0], given: 0

PS - Looking for easy calculation trick [#permalink] New post 16 Feb 2009, 20:14
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
4 students - 96
7 students - 84
4 S - 80
3 S - 70
2 S - 48

Whats median of 20S(students)?
Director
Director
avatar
Joined: 14 Aug 2007
Posts: 735
Followers: 7

Kudos [?]: 96 [0], given: 0

GMAT Tests User
Re: PS - Looking for easy calculation trick [#permalink] New post 16 Feb 2009, 20:22
84

try to arrange them in ascending order, we are intersted in 10th and 11th items, first 9: 4 S - 80 ,3 S - 70 , 2 S - 48, so 10th and 11th are from group of 84
VP
VP
User avatar
Joined: 05 Jul 2008
Posts: 1436
Followers: 33

Kudos [?]: 209 [0], given: 1

GMAT Tests User
Re: PS - Looking for easy calculation trick [#permalink] New post 20 Feb 2009, 17:10
I did not understand the Q. Can you please explain better?
Manager
Manager
User avatar
Joined: 17 Dec 2008
Posts: 179
Followers: 1

Kudos [?]: 33 [0], given: 0

Re: PS - Looking for easy calculation trick [#permalink] New post 20 Feb 2009, 17:14
I mistook median and mean... If it was mean...I was looking for an easy way to calculate it.
2 KUDOS received
Current Student
User avatar
Joined: 03 Aug 2006
Posts: 117
Location: Next to Google
Schools: Haas School of Business
Followers: 4

Kudos [?]: 98 [2] , given: 3

GMAT Tests User
Re: PS - Looking for easy calculation trick [#permalink] New post 21 Feb 2009, 01:17
2
This post received
KUDOS
There is a trick to calculate mean..it may or may not be the fastest based on the problem but its good to know. Using your example

4 x 96
7 x 84
4 x 80
3 x 70
2 x 48

Guesstimate the mean by looking at the numbers...in this case lets guess that the mean is 80.
Now subtract 80 from each number

4 x (96-80) = 4 x 16 = 64
7 x (84-80) = 7 x 4 = 28
4 x (80-80) = 4 x 0 = 0 0
3 x (70-80) = 3 x -10 = -30
2 x (48-80) = 2 x -32 = -64

Adding them (64-64+0+28-30) = -2
Divide this by 20 =-2/20 = -0.1

Now go back to the guesstimate and add this number to it = 80+(-0.1) = 80 - 0.01 = 79.9

I have gone here in much detail to explain how it works but a lot of this can be done in your mind and find a mean much faster. Hope this helps.
Expert Post
2 KUDOS received
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3604
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 349

Kudos [?]: 1683 [2] , given: 354

GMAT ToolKit User GMAT Tests User Premium Member
Re: PS - Looking for easy calculation trick [#permalink] New post 21 Feb 2009, 01:37
2
This post received
KUDOS
Expert's post
Good point, nookway
+1

There is another trick that could help you to deal with mean:

Let's say we have 3 pencils at $12.35 per pencil and 7 pencils at $12.55 per pencil. What is the mean price?

delta = 12.55 - 12.35 = 0.20

mean = 12.35+7/(3+7)*0.20=12.35+0.14=12.49

_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

2 KUDOS received
Manager
Manager
User avatar
Joined: 17 Dec 2008
Posts: 179
Followers: 1

Kudos [?]: 33 [2] , given: 0

Re: PS - Looking for easy calculation trick [#permalink] New post 21 Feb 2009, 05:28
2
This post received
KUDOS
Awesome ones, nookway and walker! +1 each. :-D
Walker, I believe your method is good for mixture problems as well? :idea:
Expert Post
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3604
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 349

Kudos [?]: 1683 [0], given: 354

GMAT ToolKit User GMAT Tests User Premium Member
Re: PS - Looking for easy calculation trick [#permalink] New post 21 Feb 2009, 06:09
Expert's post
Hm... You are right!
+1

Let's say we have 3 liters of 27.5% solution and 5 liters of 43.5% solutions. What is concentration of the mixture?

delta = 43.5-27.5 = 16.0

result = 27.5 + 5/(3+5)*16.0=37.5%

_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

VP
VP
User avatar
Joined: 05 Jul 2008
Posts: 1436
Followers: 33

Kudos [?]: 209 [0], given: 1

GMAT Tests User
Re: PS - Looking for easy calculation trick [#permalink] New post 21 Feb 2009, 08:18
walker wrote:
Hm... You are right!
+1

Let's say we have 3 liters of 27.5% solution and 5 liters of 43.5% solutions. What is concentration of the mixture?

delta = 43.5-27.5 = 16.0

result = 27.5 + 5/(3+5)*16.0=37.5%



This can be very useful. I have always hated the mixture problems.

Can you please explain how you are doing this and why you are calculating the delta?

How does this work, if there are three different solutions A,B,C?
Expert Post
1 KUDOS received
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3604
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 349

Kudos [?]: 1683 [1] , given: 354

GMAT ToolKit User GMAT Tests User Premium Member
Re: PS - Looking for easy calculation trick [#permalink] New post 22 Feb 2009, 13:29
1
This post received
KUDOS
Expert's post
Mixture 1:
x - amount
a - concentration

Mixture 2:
y - amount
b - concentration

Mixture 1+2:
z - amount
c - concentration

z= x+y
c = (a*x+b*y)/(x+y) = (a*x+a*y-a*y+b*y)/(x+y) = a + y/(x+y) * (b-a)

For A,B,C we can apply this method for any two, let's say A and B, and then we can apply the method for new mixture and C.

_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

Current Student
User avatar
Joined: 03 Aug 2006
Posts: 117
Location: Next to Google
Schools: Haas School of Business
Followers: 4

Kudos [?]: 98 [0], given: 3

GMAT Tests User
Re: PS - Looking for easy calculation trick [#permalink] New post 23 Feb 2009, 17:41
walker wrote:
Good point, nookway
+1

There is another trick that could help you to deal with mean:

Let's say we have 3 pencils at $12.35 per pencil and 7 pencils at $12.55 per pencil. What is the mean price?

delta = 12.55 - 12.35 = 0.20

mean = 12.35+7/(3+7)*0.20=12.35+0.14=12.49


That's a good one. Need to save it for future reference.

+ 1
Re: PS - Looking for easy calculation trick   [#permalink] 23 Feb 2009, 17:41
    Similar topics Author Replies Last post
Similar
Topics:
Easy Calculation Question jimmyjamesdonkey 7 23 Sep 2007, 08:44
easy ps bewakoof 4 30 Jul 2007, 18:46
easy PS anonymousegmat 7 28 Jul 2007, 14:50
PS-easy? LM 2 24 Jun 2007, 20:01
This is a straight one.. no tricks. What I am looking for is GMAThopeful 1 21 Mar 2007, 21:54
Display posts from previous: Sort by

PS - Looking for easy calculation trick

  Question banks Downloads My Bookmarks Reviews Important topics  


cron

GMAT Club MBA Forum Home| About| Privacy Policy| 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®.