1/2 + (1/2)^2 + (1/2)^3 .....(1/2)^20 is between 1/2 and 2/3 : Quant Question Archive [LOCKED]
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 19 Jan 2017, 10:30

### 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

# 1/2 + (1/2)^2 + (1/2)^3 .....(1/2)^20 is between 1/2 and 2/3

Author Message
CEO
Joined: 21 Jan 2007
Posts: 2756
Location: New York City
Followers: 11

Kudos [?]: 853 [0], given: 4

1/2 + (1/2)^2 + (1/2)^3 .....(1/2)^20 is between 1/2 and 2/3 [#permalink]

### Show Tags

06 Nov 2007, 12:48
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

1/2 + (1/2)^2 + (1/2)^3 .....(1/2)^20 is between

1/2 and 2/3
2/3 and 3/4
3/4 and 9/10
9/10 and 10/9
10/9 and 3/2

Not sure what concept this question is testing...
CEO
Joined: 21 Jan 2007
Posts: 2756
Location: New York City
Followers: 11

Kudos [?]: 853 [0], given: 4

### Show Tags

06 Nov 2007, 12:54
bmwhype2 wrote:
1/2 + (1/2)^2 + (1/2)^3 .....(1/2)^20 is between

1/2 and 2/3
2/3 and 3/4
3/4 and 9/10
9/10 and 10/9
10/9 and 3/2

Not sure what concept this question is testing...

okay nevermind. i figured it out.

the "concept" is the equation keeps adding increasingly negligible fractions as the exponents rise and the sum approaches 1. this is very similar to how limits work as they approach 0 in calculus.
Current Student
Joined: 18 Jun 2007
Posts: 408
Location: Atlanta, GA
Schools: Emory class of 2010
Followers: 11

Kudos [?]: 40 [0], given: 0

### Show Tags

06 Nov 2007, 13:02
Actually, I don't think it ever approaches 1. But you do have the concept right. I think its between 3/4 - 9/10.

Basically this is as far as you need to take it...

1/2 + 1/4 + 1/8 + 1/64 (where it becomes negligible)

3/4, then 7/8, then negligible addition from there.
CEO
Joined: 21 Jan 2007
Posts: 2756
Location: New York City
Followers: 11

Kudos [?]: 853 [0], given: 4

### Show Tags

06 Nov 2007, 13:17
emoryhopeful wrote:
Actually, I don't think it ever approaches 1. But you do have the concept right. I think its between 3/4 - 9/10.

Basically this is as far as you need to take it...

1/2 + 1/4 + 1/8 + 1/64 (where it becomes negligible)

3/4, then 7/8, then negligible addition from there.

yea. i should have clarified that. the limits never reach zero in calc, or at least that's what i remember of calculus in college.
CEO
Joined: 21 Jan 2007
Posts: 2756
Location: New York City
Followers: 11

Kudos [?]: 853 [0], given: 4

### Show Tags

06 Nov 2007, 13:23
gowani wrote:
is the OA C?

OA is D.

in C 9/10 is .90 which is less than 1. however, the sum breaks that upper bound and is constrained by 1. only D satsifies the concept.
06 Nov 2007, 13:23
Display posts from previous: Sort by