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

It is currently 01 Aug 2014, 23:12

Close

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

m22 #21

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Director
Director
avatar
Joined: 23 Apr 2010
Posts: 584
Followers: 2

Kudos [?]: 24 [0], given: 7

m22 #21 [#permalink] New post 04 Dec 2011, 05:45
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

80% (02:54) correct 20% (03:38) wrong based on 5 sessions
What is 10-8+6-4+...+(-20)?

(A) 8
(B) 10
(C) 12
(D) 14
(E) 16

Please explain how do you figure out how the sum looks like. Because I wrote the sum like this:

10 - 8 + 6 - 4 + 2 - 0 +2 -4 + 6 - 8 + 10 - 12 + 14 - 16 + 18 - 20

And I got something completely different than what's given in the question.

What's the logic behind the sum?

Thanks.
[Reveal] Spoiler: OA
1 KUDOS received
Current Student
User avatar
Status: Enjoying the MBA journey :)
Joined: 09 Sep 2011
Posts: 137
Location: United States (DC)
Concentration: General Management, Entrepreneurship
GMAT 1: 710 Q49 V38
WE: Corporate Finance (Other)
Followers: 14

Kudos [?]: 88 [1] , given: 16

GMAT Tests User
Re: m22 #21 [#permalink] New post 04 Dec 2011, 10:39
1
This post received
KUDOS
Hi

This is a simple addition/subtraction based question where the total number of digits in the expression is less and hence countable manually.
You have made a mistake considering signs on the negative side. That is the reason why your answer was different to those given in the answer options. :)

The expression considers all even numbers between 10 and -20 with alternate addition and subtraction of the numbers.
The numbers to be used are: 10, 8, 6, 4, 2, 0, -2, -4, -6, -8, -10, -12, -14, -16, -18 and -20.

Now, the first term is positive and the next term is subtracted. So, the required expression becomes,

10 - 8 + 6 - 4 + 2 - 0 + (-2) - (-4) + (-6) - (-8) + (-10) - (-12) + (-14) - (-16) + (-18) - (-20)
= 10 - 8 + 6 - 4 + 2 - 0 - 2 + 4 - 6 + 8 - 10 + 12 - 14 + 16 - 18 + 20
= 78 - 62
= 16

Hence the correct answer choice is E.
_________________

MBA Candidate 2015 | Georgetown University
McDonough School of Business

Director
Director
avatar
Joined: 23 Apr 2010
Posts: 584
Followers: 2

Kudos [?]: 24 [0], given: 7

Re: m22 #21 [#permalink] New post 05 Dec 2011, 05:19
Quote:
The expression considers all even numbers between 10 and -20 with alternate addition and subtraction of the numbers.


Thanks. Got it. I think it'd be better if a couple of last numbers in the sequence were indicated.
Re: m22 #21   [#permalink] 05 Dec 2011, 05:19
    Similar topics Author Replies Last post
Similar
Topics:
m22 #21 LM 2 09 May 2010, 12:44
32 Experts publish their posts in the topic m22#30 ventivish 35 26 Nov 2008, 20:27
55 Experts publish their posts in the topic M22#16 ventivish 18 26 Nov 2008, 19:17
8 Experts publish their posts in the topic m22#3 ventivish 20 26 Nov 2008, 18:54
7 Experts publish their posts in the topic M22 #10 snowy2009 15 02 Oct 2008, 11:20
Display posts from previous: Sort by

m22 #21

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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®.