It is currently 23 Sep 2017, 09:52

Happening Now:

Alleviate MBA app anxiety! Come to Chat Room #2


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.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

What is the average (arithmetic mean) of all multiples of 10

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

BSchool Forum Moderator
User avatar
Status: Flying over the cloud!
Joined: 17 Aug 2011
Posts: 895

Kudos [?]: 709 [0], given: 44

Location: Viet Nam
Concentration: International Business, Marketing
GMAT Date: 06-06-2014
GPA: 3.07
GMAT ToolKit User Premium Member Reviews Badge
What is the average (arithmetic mean) of all multiples of 10 [#permalink]

Show Tags

New post 13 Oct 2015, 11:10
1
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

76% (00:45) correct 24% (00:49) wrong based on 107 sessions

HideShow timer Statistics

What is the average (arithmetic mean) of all multiples of 10 from 10 to 400 inclusive?

(A) 190

(B) 195

(C) 200

(D) 205

(E) 210
[Reveal] Spoiler: OA

_________________

Rules for posting in verbal gmat forum, read it before posting anything in verbal forum
Giving me + 1 kudos if my post is valuable with you :)

The more you like my post, the more you share to other's need

CR: Focus of the Week: Must be True Question

Kudos [?]: 709 [0], given: 44

Expert Post
1 KUDOS received
Math Forum Moderator
avatar
B
Joined: 20 Mar 2014
Posts: 2684

Kudos [?]: 1688 [1], given: 792

Concentration: Finance, Strategy
Schools: Kellogg '18 (M)
GMAT 1: 750 Q49 V44
GPA: 3.7
WE: Engineering (Aerospace and Defense)
GMAT ToolKit User Premium Member Reviews Badge
Re: What is the average (arithmetic mean) of all multiples of 10 [#permalink]

Show Tags

New post 13 Oct 2015, 11:33
1
This post received
KUDOS
Expert's post
1
This post was
BOOKMARKED
tuanquang269 wrote:
What is the average (arithmetic mean) of all multiples of 10 from 10 to 400 inclusive?

(A) 190

(B) 195

(C) 200

(D) 205

(E) 210



This question is straightforward if you realise that the question asks the average of 10,20,30....390,400 . As this is an arithmetic progression, the sum of the series will be = S = \(\frac{n[a+a_n]}{2}\), where n = number of terms= (400-10)/10+1 = 39+1 = 40, a= 1st term =10 and \(a_n\) = last term = 400

Also, average = Sum / number of terms = S/n = \(\frac{n[a+a_n]}{2*n}\) = \(\frac{[a+a_n]}{2}\) = (10+400)/2 = 410/2 = 205.

D is the correct answer.

Hope this helps.
_________________

Thursday with Ron updated list as of July 1st, 2015: http://gmatclub.com/forum/consolidated-thursday-with-ron-list-for-all-the-sections-201006.html#p1544515
Rules for Posting in Quant Forums: http://gmatclub.com/forum/rules-for-posting-please-read-this-before-posting-133935.html
Writing Mathematical Formulae in your posts: http://gmatclub.com/forum/rules-for-posting-please-read-this-before-posting-133935.html#p1096628
GMATCLUB Math Book: http://gmatclub.com/forum/gmat-math-book-in-downloadable-pdf-format-130609.html
Everything Related to Inequalities: http://gmatclub.com/forum/inequalities-made-easy-206653.html#p1582891
Inequalities tips: http://gmatclub.com/forum/inequalities-tips-and-hints-175001.html
Debrief, 650 to 750: http://gmatclub.com/forum/650-to-750-a-10-month-journey-to-the-score-203190.html

Kudos [?]: 1688 [1], given: 792

Expert Post
EMPOWERgmat Instructor
User avatar
P
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 9809

Kudos [?]: 3317 [0], given: 171

Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Re: What is the average (arithmetic mean) of all multiples of 10 [#permalink]

Show Tags

New post 13 Oct 2015, 23:19
Hi tuanquang269,

This question can be solved with the Average Formula and 'bunching.'

We're asked for the average of all of the multiples of 10 from 10 to 400, inclusive.

To start, we can figure out the total number of terms rather easily:
1(10) = 10
2(10) = 20
...
40(10) = 400

So we know that there are 40 total numbers.

We can now figure out the SUM of those numbers with 'bunching':

10 + 400 = 410
20 + 390 = 410
30 + 380 = 410
Etc.

Since there are 40 total terms, this pattern will create 20 'pairs' of 410.

Thus, since the average = (Sum of terms)/(Number of terms), we have...

(20)(410)/(40) =
410/2 =
205

Final Answer:
[Reveal] Spoiler:
D


GMAT assassins aren't born, they're made,
Rich
_________________

760+: Learn What GMAT Assassins Do to Score at the Highest Levels
Contact Rich at: Rich.C@empowergmat.com

Rich Cohen

Co-Founder & GMAT Assassin

Special Offer: Save $75 + GMAT Club Tests Free

Official GMAT Exam Packs + 70 Pt. Improvement Guarantee
www.empowergmat.com/

***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************

Kudos [?]: 3317 [0], given: 171

Manager
Manager
avatar
B
Joined: 08 Jun 2017
Posts: 69

Kudos [?]: 1 [0], given: 24

Re: What is the average (arithmetic mean) of all multiples of 10 [#permalink]

Show Tags

New post 16 Aug 2017, 23:42
Hi Bunuel but can v do it wth ur approach of multiplying with K i.e 10

Kudos [?]: 1 [0], given: 24

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 41698

Kudos [?]: 124614 [0], given: 12079

Re: What is the average (arithmetic mean) of all multiples of 10 [#permalink]

Show Tags

New post 16 Aug 2017, 23:58
Asac123 wrote:
What is the average (arithmetic mean) of all multiples of 10 from 10 to 400 inclusive?

(A) 190

(B) 195

(C) 200

(D) 205

(E) 210

Hi Bunuel but can v do it wth ur approach of multiplying with K i.e 10


Not sure which method you are referring to but probably the easiest way would be to realise that multiples of 10 create an evenly spaced set (aka Arithmetic Progression). For any evenly spaced set the mean is the average of the first and last terms, so it's (10 + 400)/2 = 205.

Answer: D.

Hope it helps.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 124614 [0], given: 12079

Manager
Manager
avatar
B
Joined: 08 Jun 2017
Posts: 69

Kudos [?]: 1 [0], given: 24

Re: What is the average (arithmetic mean) of all multiples of 10 [#permalink]

Show Tags

New post 17 Aug 2017, 08:00
Bunuel wrote:
Asac123 wrote:
What is the average (arithmetic mean) of all multiples of 10 from 10 to 400 inclusive?

(A) 190

(B) 195

(C) 200

(D) 205

(E) 210

Hi Bunuel but can v do it wth ur approach of multiplying with K i.e 10


Not sure which method you are referring to but probably the easiest way would be to realise that multiples of 10 create an evenly spaced set (aka Arithmetic Progression). For any evenly spaced set the mean is the average of the first and last terms, so it's (10 + 400)/2 = 205.

Answer: D.

Hope it helps.


If alist gets multiplied by K then mean also gets multiplied by K?

Kudos [?]: 1 [0], given: 24

Re: What is the average (arithmetic mean) of all multiples of 10   [#permalink] 17 Aug 2017, 08:00
    Similar topics Author Replies Last post
Similar
Topics:
33 EXPERTS_POSTS_IN_THIS_TOPIC If m is the average (arithmetic mean) of the first 10 BANON 16 11 Jun 2017, 06:58
11 EXPERTS_POSTS_IN_THIS_TOPIC The average (arithmetic mean) of the multiples of 6 perseverant 7 01 Mar 2017, 18:19
1 EXPERTS_POSTS_IN_THIS_TOPIC What is the average (arithmetic mean) of all solutions to the equation Bunuel 5 15 Feb 2017, 16:16
1 EXPERTS_POSTS_IN_THIS_TOPIC If m is the average (arithmetic mean) of the first 10 positive multipl Bunuel 4 31 Dec 2016, 04:11
3 EXPERTS_POSTS_IN_THIS_TOPIC What is the average (arithmetic mean) of all the multiples of ten from Bunuel 7 15 May 2017, 17:29
Display posts from previous: Sort by

What is the average (arithmetic mean) of all multiples of 10

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.