It is currently 16 Oct 2017, 23:51

### 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

# 2^2 - 4^2 + 6^2 - 8^2 + 10^2 - 12^2 + 14^2 - 16^2 + 18^2

 Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:
GRE Instructor
Joined: 10 Apr 2015
Posts: 637
Followers: 29

Kudos [?]: 449 [1] , given: 3

2^2 - 4^2 + 6^2 - 8^2 + 10^2 - 12^2 + 14^2 - 16^2 + 18^2 [#permalink]  06 Jun 2017, 13:08
1
This post received
KUDOS
Expert's post
00:00

Difficulty:

5% (low)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
2^2 - 4^2 + 6^2 - 8^2 + 10^2 - 12^2 + 14^2 - 16^2 + 18^2 - 20^2 =

A) -40
B) -110
C) -220
D) -440
E) -880
[Reveal] Spoiler: OA

_________________

Brent Hanneson – Founder of greenlighttestprep.com

Check out the online reviews of our course

GRE Instructor
Joined: 10 Apr 2015
Posts: 637
Followers: 29

Kudos [?]: 449 [1] , given: 3

Re: 2^2 - 4^2 + 6^2 - 8^2 + 10^2 - 12^2 + 14^2 - 16^2 + 18^2 [#permalink]  07 Jun 2017, 15:06
1
This post received
KUDOS
Expert's post
GreenlightTestPrep wrote:
2^2 - 4^2 + 6^2 - 8^2 + 10^2 - 12^2 + 14^2 - 16^2 + 18^2 - 20^2 =

A) -40
B) -110
C) -220
D) -440
E) -880

Here's an approach that uses differences of squares

2² - 4² + 6² - 8² + 10² - 12² + 14² - 16² + 18² - 20² = (2² - 4²) + (6² - 8²) + (10² - 12²) + (14² - 16²) + (18² - 20²)
= (2 - 4)(2 + 4) + (6 - 8)(6 + 8) + (10 - 12)(10 + 12) + (14 - 16)(14 + 16) + (18 - 20)(18 + 20)
= (-2)(2 + 4) + (-2)(6 + 8) + (-2)(10 + 12) + (-2)(14 + 16) + (-2)(18 + 20)
= -2(2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20)
= -2(2)(1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10)
= (-4)(1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10)
= (-4)(55)
= -220

Answer:
[Reveal] Spoiler:
C

Cheers,
Brent
_________________

Brent Hanneson – Founder of greenlighttestprep.com

Check out the online reviews of our course

Re: 2^2 - 4^2 + 6^2 - 8^2 + 10^2 - 12^2 + 14^2 - 16^2 + 18^2   [#permalink] 07 Jun 2017, 15:06
Display posts from previous: Sort by

# 2^2 - 4^2 + 6^2 - 8^2 + 10^2 - 12^2 + 14^2 - 16^2 + 18^2

 Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group Kindly note that the GRE® test is a registered trademark of the Educational Testing Service®, and this site has neither been reviewed nor endorsed by ETS®.