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

 It is currently 03 May 2015, 05:43

### 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

# 2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = 2^9 2^10

Author Message
TAGS:
Intern
Joined: 11 Oct 2004
Posts: 6
Location: Georgia
Followers: 0

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

2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 = 2^9 2^10 [#permalink]  14 Jun 2006, 16:19
2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8 =

2^9

2^10

2^16

2^35

Exponents are not my forte. I cannot see the rule suppose to apply.
Thought of trying to factor out a common term but did not help

Got it wrong on the test after reviewing can see there is a pattern.

2 + 2 + 2^2 + 2^3 + â€¦â€¦.+ 2^6

= 2^7

What level of difficulty would you rate this question.

Thanks.
VP
Joined: 02 Jun 2006
Posts: 1267
Followers: 2

Kudos [?]: 42 [0], given: 0

2^9... don't know about level of difficulty... should rate it somewhere below medium, but I am sure other will correct me just in case...
Manager
Joined: 29 Sep 2005
Posts: 125
Followers: 1

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

2^9 as well.

Approach was just looking at terms and finding the pattern i.e. 2*2^3....etc etc.

Difficulty would definitely be between medium and easy. Leaning more towards the easy.
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5078
Location: Singapore
Followers: 22

Kudos [?]: 184 [0], given: 0

Here's how i would solve it.

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

= 2^4 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8

= 2^6 + 2^6 + 2^7 + 2^8

= 2^8 + 2^8

= 2^9

Level of difficulty should be slightly below mid range, i guess....
Director
Joined: 06 May 2006
Posts: 781
Followers: 3

Kudos [?]: 16 [0], given: 0

Mmmm..

2 + (2 + 2^2 + 2^3 + ... + 2^8)
= 2 + (sum of first 8 terms of GP with initial value 2 and common multiplying factor 2)
= 2 + [2 x (2^8 - 1)/(2 - 1)]
= 2 + 2^9 - 2
= 2^9

Definitely easy. Once you spot the GP, that is...
Similar topics Replies Last post
Similar
Topics:
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 = a) 2^9 b) 3 10 Dec 2007, 11:54
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 = ? 1) 2^9 9 29 May 2006, 15:46
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