GMAT Prep PS sequence : PS Archive
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 21 Jan 2017, 14:01

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# GMAT Prep PS sequence

Author Message
Manager
Joined: 19 Oct 2008
Posts: 95
Followers: 1

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

### Show Tags

15 Mar 2009, 12:31
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

### HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

For every integer K from 1-10 inclusive kth term of a certain sequence is given by (-1)^K+1 .(1/2^K) . If T is the sum of the first 10 terms in a sequence, then T is

A. Greater than 2
B. Between 1 & 2
C. Between 1/2 & 1
D. Between 1/4 & 1/2
E. Less than 1/4

Can you please let me know how to solve it less than 2 minutes?
Manager
Joined: 19 Oct 2008
Posts: 95
Followers: 1

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

Re: GMAT Prep PS sequence [#permalink]

### Show Tags

16 Mar 2009, 04:31
Never mind, solved it:

5th term = (-1/2)^6*(1/2^5)=1/32
6th term = (-1/2)^7*(1/2^6)=-1/64
Average of the two= 1/32
Sum of 10 terms= 10*1/32=5/16----31% or between 1/4(25%) and 1/2(50%)

Is there any other quick approach?
Intern
Joined: 21 Jul 2006
Posts: 18
Followers: 0

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

Re: GMAT Prep PS sequence [#permalink]

### Show Tags

14 Apr 2009, 18:19
First find the r by plugging k as 1 and 2, in this case -1/2
since |r|<1, we can use the GP formula a/(1- r)
which in this case gives 1/3.

Re: GMAT Prep PS sequence   [#permalink] 14 Apr 2009, 18:19
Display posts from previous: Sort by