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

 It is currently 14 Sep 2014, 20:13

### 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

# Events & Promotions

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

# 2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = ? 1) 2^9

 Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:
Manager
Joined: 10 May 2006
Posts: 186
Location: USA
Followers: 1

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

2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = ? 1) 2^9 [#permalink]  29 May 2006, 15:46
2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = ?

1) 2^9
2) 2^10
3) 2^16
4) 2^35
5) 2^37
Manager
Joined: 19 Apr 2006
Posts: 231
Followers: 1

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

Re: Exponents [#permalink]  29 May 2006, 15:53
tl372 wrote:
2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = ?

1) 2^9
2) 2^10
3) 2^16
4) 2^35
5) 2^37

I think this is one of those tricky question...
I would first factor out 2^8 from the whole equation... I will then get

2^8*(2^-7+2^-7+2^-6+2^-5+2^-4+2^-3+(1/4)+(1/2)+1)

the value in read a small enought that they can be considered or assumed to be zeros. So 2^9 would the be logical answer.

A is my answer
Senior Manager
Joined: 15 Mar 2005
Posts: 425
Location: Phoenix
Followers: 1

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

Re: Exponents [#permalink]  29 May 2006, 16:39
Its like the sum of an infinite Geometric progression with an r of 1/2.
The answer is 2^9 if the series is 2^8+2^7+2^6+...+2^2+2^1+2^0

Since the given series is 2^2+2^1+2^0+1, the sum of the series is 2^9+1.

However since that answer is not provided, I'd go with A.
_________________

Who says elephants can't dance?

VP
Joined: 29 Dec 2005
Posts: 1351
Followers: 6

Kudos [?]: 28 [0], given: 0

Re: Exponents [#permalink]  29 May 2006, 20:29
tl372 wrote:
2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = ?

1) 2^9
2) 2^10
3) 2^16
4) 2^35
5) 2^37

=2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8
=2^2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8
=2^3 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8
=2^4 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8
=2^5 + 2^5 + 2^6 + 2^7 + 2^8
.
.
.
.
=2^8 + 2^8 = 2^9
Manager
Joined: 25 May 2006
Posts: 227
Followers: 1

Kudos [?]: 14 [0], given: 0

[#permalink]  29 May 2006, 20:39
I also got A)

=2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8
=4+4+8+16+32+64+128+256=512=256*2=2^9

It shouldnâ€™t take you more than 30 sec to sum (4+8+16...+256)

You can check the 2^9 by doing prime factorization of 512, but I think this problem is more of logic than of doing operations.

Cheers!!
SVP
Joined: 30 Mar 2006
Posts: 1741
Followers: 1

Kudos [?]: 26 [0], given: 0

[#permalink]  29 May 2006, 21:54
A for me too.......

2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8
=> 2(1+1+2+ 2^3 + 2^4 + 2^5 + 2^6 + 2^7)
=>2(2+2+ 2^3 + 2^4 + 2^5 + 2^6 + 2^7)

if you see the pattern here, you will come to the answer
Manager
Joined: 04 May 2006
Posts: 53
Followers: 1

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

[#permalink]  30 May 2006, 04:34
A for me too.. same approach as prof's..
Manager
Joined: 12 Feb 2006
Posts: 117
Followers: 1

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

[#permalink]  30 May 2006, 04:49
I have a question on this.

If 2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = 2^9

Then does If 2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 + 2^9 = 2^10?

I think that is how I see it using both the Profs and X and Y's approach.
Manager
Joined: 10 May 2006
Posts: 186
Location: USA
Followers: 1

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

[#permalink]  30 May 2006, 05:47
OA is A. Great expanations guys. Thanks.
Manager
Joined: 11 Oct 2005
Posts: 94
Followers: 1

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

[#permalink]  03 Jun 2006, 14:24
Late A for me same approach as proffs
[#permalink] 03 Jun 2006, 14:24
Similar topics Replies Last post
Similar
Topics:
2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 ? a) 2^9 b) 8 04 Jul 2008, 12:18
2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = 2^9 2^10 6 12 Apr 2008, 11:37
2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8= 2^9 4 27 Sep 2006, 07:27
2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = 2^9 2^10 4 14 Jun 2006, 16:19
2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 a. 2^9 b. 4 04 May 2006, 14:53
Display posts from previous: Sort by

# 2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = ? 1) 2^9

 Question banks Downloads My Bookmarks Reviews Important topics

 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®.