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

It is currently 31 Jul 2014, 20:02

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-Prep, time killer

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Senior Manager
Senior Manager
User avatar
Joined: 29 Nov 2006
Posts: 321
Location: Orange County, CA
Followers: 1

Kudos [?]: 19 [0], given: 0

GMAT Tests User
PS-Prep, time killer [#permalink] New post 28 Jun 2007, 08:19
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
Any suggestions for a quicker answer?

I was taking too long determining sign changes and adding / subtracting between each item (1-10) and ended up just guessing in order to move onto the next problem.

Looking for ways to cut down time on easy questions like this.
Attachments

Quant_time eater_20070628.doc [60 KiB]
Downloaded 84 times

To download please login or register as a user

VP
VP
User avatar
Joined: 08 Jun 2005
Posts: 1157
Followers: 6

Kudos [?]: 106 [0], given: 0

GMAT Tests User
 [#permalink] New post 28 Jun 2007, 09:38
using Geometric Progression formula is shorter but easy to make mistakes:

Sn = a(1-R^n)/(1-R)

n = 10
a = 1/2

F(1) = 1/2
F(2) = -1/4
F(3) = 1/8

hence R = -1/2

solve GP

Sn = 1/2*(1-(-1/2^10))/(1-(-1/2))

Sn = (1025/2048)/(3/2)

Sn = 2050/2048/3

Sn = ~1/3

the answer is (D)

:-D
CIO
CIO
User avatar
Joined: 09 Mar 2003
Posts: 466
Followers: 1

Kudos [?]: 24 [0], given: 0

GMAT Tests User
Re: PS-Prep, time killer [#permalink] New post 28 Jun 2007, 11:06
misterJJ2u wrote:
Any suggestions for a quicker answer?

I was taking too long determining sign changes and adding / subtracting between each item (1-10) and ended up just guessing in order to move onto the next problem.

Looking for ways to cut down time on easy questions like this.


Also D. 1 minute.

1. Find pattern. There has to be one, otherwise it wouldn't be a GMAT question. Very quickly see that this thing is just alternating positive and negative powers of 1/2:
1/2, -1/4, 1/8, -1/16....

2. Every change is smaller than the previous one. Classic GMAT game. I drew a number line:

-|---------------------|----------------------|
0 ....................... 1/4 ..................... 1/2

Numbers start at 1/2, then down 1/4, then up 1/8, then down 1/16. You basically bounce back and fourth, but you NEVER cross 1/4, and you never cross 1/2.

-|---------------------|----------------------|
0 ....................... 1/4 ..................... 1/2
...................................................... Start
............................ {---------------------- ....(Back 1/4)
............................. ------------} ...............(forward 1/8)
......................................{----- ................(back 1/16)
.......................................---} .................(forward 1/32)
....................................... {- .................. (back 1/64)

Etc, etc. It's a lot here to type out, on paper, really simple. Either way, you can see the range you're in pretty clearly.
VP
VP
User avatar
Joined: 08 Jun 2005
Posts: 1157
Followers: 6

Kudos [?]: 106 [0], given: 0

GMAT Tests User
Re: PS-Prep, time killer [#permalink] New post 28 Jun 2007, 11:25
ian7777 wrote:
misterJJ2u wrote:
Any suggestions for a quicker answer?

I was taking too long determining sign changes and adding / subtracting between each item (1-10) and ended up just guessing in order to move onto the next problem.

Looking for ways to cut down time on easy questions like this.


Also D. 1 minute.

1. Find pattern. There has to be one, otherwise it wouldn't be a GMAT question. Very quickly see that this thing is just alternating positive and negative powers of 1/2:
1/2, -1/4, 1/8, -1/16....

2. Every change is smaller than the previous one. Classic GMAT game. I drew a number line:

-|---------------------|----------------------|
0 ....................... 1/4 ..................... 1/2

Numbers start at 1/2, then down 1/4, then up 1/8, then down 1/16. You basically bounce back and fourth, but you NEVER cross 1/4, and you never cross 1/2.

-|---------------------|----------------------|
0 ....................... 1/4 ..................... 1/2
...................................................... Start
............................ {---------------------- ....(Back 1/4)
............................. ------------} ...............(forward 1/8)
......................................{----- ................(back 1/16)
.......................................---} .................(forward 1/32)
....................................... {- .................. (back 1/64)

Etc, etc. It's a lot here to type out, on paper, really simple. Either way, you can see the range you're in pretty clearly.


Nice ! - Thanks for your help - I'm guessing its a lot of work to write it all down. A true and elegant solution.

:)
Director
Director
User avatar
Joined: 26 Feb 2006
Posts: 908
Followers: 3

Kudos [?]: 36 [0], given: 0

GMAT Tests User
Re: PS-Prep, time killer [#permalink] New post 28 Jun 2007, 11:33
ian7777 wrote:
misterJJ2u wrote:
Any suggestions for a quicker answer?

I was taking too long determining sign changes and adding / subtracting between each item (1-10) and ended up just guessing in order to move onto the next problem.

Looking for ways to cut down time on easy questions like this.


Also D. 1 minute.

1. Find pattern. There has to be one, otherwise it wouldn't be a GMAT question. Very quickly see that this thing is just alternating positive and negative powers of 1/2:
1/2, -1/4, 1/8, -1/16....

2. Every change is smaller than the previous one. Classic GMAT game. I drew a number line:

-|---------------------|----------------------|
0 ....................... 1/4 ..................... 1/2

Numbers start at 1/2, then down 1/4, then up 1/8, then down 1/16. You basically bounce back and fourth, but you NEVER cross 1/4, and you never cross 1/2.

-|---------------------|----------------------|
0 ....................... 1/4 ..................... 1/2
...................................................... Start
............................ {---------------------- ....(Back 1/4)
............................. ------------} ...............(forward 1/8)
......................................{----- ................(back 1/16)
.......................................---} .................(forward 1/32)
....................................... {- .................. (back 1/64)

Etc, etc. It's a lot here to type out, on paper, really simple. Either way, you can see the range you're in pretty clearly.


wonderful approach..


btw, i got 341/1024 using my lengthy approach..
Senior Manager
Senior Manager
User avatar
Joined: 29 Nov 2006
Posts: 321
Location: Orange County, CA
Followers: 1

Kudos [?]: 19 [0], given: 0

GMAT Tests User
 [#permalink] New post 28 Jun 2007, 11:55
Quote:

Also D. 1 minute.

1. Find pattern. There has to be one, otherwise it wouldn't be a GMAT question. Very quickly see that this thing is just alternating positive and negative powers of 1/2:
1/2, -1/4, 1/8, -1/16....

2. Every change is smaller than the previous one. Classic GMAT game. I drew a number line:

-|---------------------|----------------------|
0 ....................... 1/4 ..................... 1/2

Numbers start at 1/2, then down 1/4, then up 1/8, then down 1/16. You basically bounce back and fourth, but you NEVER cross 1/4, and you never cross 1/2.

-|---------------------|----------------------|
0 ....................... 1/4 ..................... 1/2
...................................................... Start
............................ {---------------------- ....(Back 1/4)
............................. ------------} ...............(forward 1/8)
......................................{----- ................(back 1/16)
.......................................---} .................(forward 1/32)
....................................... {- .................. (back 1/64)

Etc, etc. It's a lot here to type out, on paper, really simple. Either way, you can see the range you're in pretty clearly.


Thanks Ian. That's exactly what I was looking for. I figured there was some easier way. Now I just have to be able to find it and apply it on test day! :)
Manager
Manager
User avatar
Joined: 14 Mar 2007
Posts: 240
Followers: 1

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

GMAT Tests User
 [#permalink] New post 28 Jun 2007, 12:25
my aproach to this question:

first try 3 consecutive numbers

for k =1 : 0.5
for k=2 : -0.25
for k=3 : 0.125

so we have a geometric progression with ratio 1/-2....with this you can get your answer in less than 1minut
  [#permalink] 28 Jun 2007, 12:25
    Similar topics Author Replies Last post
Similar
Topics:
1 EMBA is a killer RVD 14 15 Jun 2008, 22:41
PS-prep LM 1 23 Jun 2007, 23:46
PS-prep LM 3 23 Jun 2007, 23:45
PS-prep LM 1 23 Jun 2007, 23:40
Sometimes easy questions may be time killers idue to the Yurik79 7 08 Nov 2006, 09:45
Display posts from previous: Sort by

PS-Prep, time killer

  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®.