GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 10 Dec 2018, 18:56

### 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 December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
• ### Free lesson on number properties

December 10, 2018

December 10, 2018

10:00 PM PST

11:00 PM PST

Practice the one most important Quant section - Integer properties, and rapidly improve your skills.
• ### Free GMAT Prep Hour

December 11, 2018

December 11, 2018

09:00 PM EST

10:00 PM EST

Strategies and techniques for approaching featured GMAT topics. December 11 at 9 PM EST.

# What is the sum of the multiples of 7 from 84 to 140, inclus

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

### Hide Tags

Director
Joined: 03 Sep 2006
Posts: 789
What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

Updated on: 22 Jul 2013, 10:01
5
17
00:00

Difficulty:

25% (medium)

Question Stats:

76% (01:41) correct 24% (02:06) wrong based on 523 sessions

### HideShow timer Statistics

What is the sum of the multiples of 7 from 84 to 140, inclusive?

A. 896
B. 963
C. 1008
D, 1792
E. 2016

Originally posted by LM on 23 May 2007, 19:47.
Last edited by Bunuel on 22 Jul 2013, 10:01, edited 1 time in total.
Renamed the topic, edited the question and added the OA.
##### Most Helpful Expert Reply
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8656
Location: Pune, India
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

22 Jul 2013, 21:44
12
LM wrote:
What is the sum of the multiples of 7 from 84 to 140, inclusive?

A. 896
B. 963
C. 1008
D, 1792
E. 2016

Alternatively, note that 84 = 7*12 and 140 = 7*20

7*12 + 7*13 + ... 7*20 = 7*(12 + 13 + 14 .. + 20)
12 to 20 are 9 consecutive numbers so their sum will be (middle number) * 9 = 16*9 = 144

Total sum = 7*144 = 1008
_________________

[b]Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >

##### General Discussion
Director
Joined: 26 Feb 2006
Posts: 859
Re: PS  [#permalink]

### Show Tags

23 May 2007, 20:35
1
1
LM wrote:
What is the sum of the multiples of 7 from 84 to 140, inclusive?
896
963
1008
1792
2016

Please explain some FAST SHORT method

= [(140 + 84)/2] [(140/7) - (84/7 + (1)]
= 1008
Director
Joined: 03 Sep 2006
Posts: 789
Re: PS  [#permalink]

### Show Tags

23 May 2007, 20:55
Himalayan wrote:
LM wrote:
What is the sum of the multiples of 7 from 84 to 140, inclusive?
896
963
1008
1792
2016

Please explain some FAST SHORT method

= [(140 + 84)/2] [(140/7) - (84/7 + (1)]
= 1008

Wonderful!!! Thanks a lot!! Could you please explain too?
Director
Joined: 03 Sep 2006
Posts: 789
Re: PS  [#permalink]

### Show Tags

23 May 2007, 21:00
LM wrote:
Himalayan wrote:
LM wrote:
What is the sum of the multiples of 7 from 84 to 140, inclusive?
896
963
1008
1792
2016

Please explain some FAST SHORT method

= [(140 + 84)/2] [(140/7) - (84/7 + (1)]
= 1008

Wonderful!!! Thanks a lot!! Could you please explain too?

Okayyy I got it!! you are using AP series formula!!
Manager
Joined: 13 Feb 2007
Posts: 63
simpler method  [#permalink]

### Show Tags

23 May 2007, 22:57
1
all you have to do on a quick test like gmat is this:

84, 91, 98, 105, 112, 119, 126, 133, 140.

i wouldn't even list 'em out on the test.

(84 + 140) / 4.5 = answer
Director
Joined: 03 Sep 2006
Posts: 789
Re: simpler method  [#permalink]

### Show Tags

26 May 2007, 18:17
ethan_casta wrote:
all you have to do on a quick test like gmat is this:

84, 91, 98, 105, 112, 119, 126, 133, 140.

i wouldn't even list 'em out on the test.

(84 + 140) / 4.5 = answer

What is 4.5? Why are you dividing by 4.5 and where did you get that? How do you reach the answer with your method in short time.
Intern
Joined: 26 Jun 2012
Posts: 24
Location: Germany
Concentration: Leadership, Finance
GMAT 1: 570 Q31 V39
GMAT 2: 710 Q43 V44
Re: What is the sum of the multiples of 7 from 84 to 140,  [#permalink]

### Show Tags

22 Jul 2013, 09:57
3
You could also add up the last digit of the multiples:

4 + 1 + 8 + 5 + 2 + 9 + 6 + 3 + 0 = ..8 --> last digit of solution must be 8 --> 1008 --> Answer C
Intern
Joined: 26 Jun 2012
Posts: 24
Location: Germany
Concentration: Leadership, Finance
GMAT 1: 570 Q31 V39
GMAT 2: 710 Q43 V44
Re: What is the sum of the multiples of 7 from 84 to 140,  [#permalink]

### Show Tags

22 Jul 2013, 09:59
By the way,

Difficulty: 500-600
Tag: Consecutive Integers
Source: Manhattan GMAT
OA:
Answer C
Intern
Joined: 25 May 2012
Posts: 6
Location: United States
Concentration: Finance
WE: Corporate Finance (Non-Profit and Government)
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

22 Jul 2013, 12:19
2
2
The formula we want to use in this type of problem is this:
Average*Total Numbers=Sum

First, find the average by taking the sum of the F + L number and divide it by 2:
A = (F + L)/2

Second, find the total numbers in our range by dividing our F and L numbers by 7 and add 1.
(140/7) - (84/7) + 1

Multiply these together so what we show Average*Total Numbers=Sum
(84 + 140)/2 * (140/7) - (84/7) + 1 = Sum
112 * 9 = 1008
C
Manager
Joined: 22 Apr 2013
Posts: 81
Re: simpler method  [#permalink]

### Show Tags

07 Aug 2013, 06:41
1
1
LM wrote:
ethan_casta wrote:
all you have to do on a quick test like gmat is this:

84, 91, 98, 105, 112, 119, 126, 133, 140.

i wouldn't even list 'em out on the test.

(84 + 140) / 4.5 = answer

What is 4.5? Why are you dividing by 4.5 and where did you get that? How do you reach the answer with your method in short time.

It's multiply by 4.5. (84 + 140) * 9/2 == 224*4.5 == 1008 The 9 in the formula is the number of consecutive items in the list.
_________________

I do not beg for kudos.

Senior Manager
Joined: 10 Jul 2013
Posts: 315
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

07 Aug 2013, 09:10
1
LM wrote:
What is the sum of the multiples of 7 from 84 to 140, inclusive?

A. 896
B. 963
C. 1008
D, 1792
E. 2016

solution;
(140-84)/7 = 8
so total number = 8+1 = 9
summation= 9/2 {2*84+(9-1)*7} = 1008 = C
_________________

Asif vai.....

Intern
Joined: 05 Apr 2010
Posts: 12
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

07 Aug 2013, 09:28
1
Asifpirlo wrote:
LM wrote:
What is the sum of the multiples of 7 from 84 to 140, inclusive?

A. 896
B. 963
C. 1008
D, 1792
E. 2016

solution;
(140-84)/7 = 8
so total number = 8+1 = 9
summation= 9/2 {2*84+(9-1)*7} = 1008 = C

All perfect till no of terms. I suggest following for sum.
sum = number of terms * (avg of first and last term) = 9 * (84+140)/2 = 1008.

May help save a second or two.
Manager
Joined: 23 Jan 2013
Posts: 142
Concentration: Technology, Other
Schools: Berkeley Haas
GMAT Date: 01-14-2015
WE: Information Technology (Computer Software)
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

31 Mar 2014, 10:48
All numbers are consecutive and with a spacing of 7 .

So average would be (140 + 84 )/2 = 112 .

Sum of 9 numbers = 9 * average = 9 * 112 = 1008
Senior Manager
Status: Math is psycho-logical
Joined: 07 Apr 2014
Posts: 419
Location: Netherlands
GMAT Date: 02-11-2015
WE: Psychology and Counseling (Other)
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

13 Feb 2015, 11:20
If it doesn't occur to us to use the (first+last)/2 we can always go up 7, starting with 84 until 140. Adding them up wouldn't take longer. That if panic hits and we cannot think of the easiest way, which I guess would be "(first+last)/2".

(first+last)/2 --> gives the mean.
we know that 9 is the N.

So, we then use:
M= S/N --> 112 = S / 9 --> S = 9*112 --> S = 1008.
Intern
Joined: 16 Jan 2016
Posts: 19
Location: United States (CA)
Leonid: B
Concentration: Operations, General Management
GPA: 3.6
WE: Operations (Other)
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

05 Sep 2016, 18:10
I do not get the 4.5 part??

all you have to do on a quick test like gmat is this:

84, 91, 98, 105, 112, 119, 126, 133, 140.

i wouldn't even list 'em out on the test.

(84 + 140) / 4.5 = answer

Can someone please explain this?
_________________

I Write...

http://www.misterethoughts.blogspot.com

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8656
Location: Pune, India
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

05 Sep 2016, 21:23
leonidbasin1 wrote:
I do not get the 4.5 part??

all you have to do on a quick test like gmat is this:

84, 91, 98, 105, 112, 119, 126, 133, 140.

i wouldn't even list 'em out on the test.

(84 + 140) / 4.5 = answer

Can someone please explain this?

This is incorrect.
The concept used is
Sum = Average * Number of elements

Average = (84+140)/2
Number of elements = 9

Sum = [(84+140)/2] * 9 = (84 + 140) * 4.5 = 1008
_________________

[b]Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >

Director
Joined: 04 Jun 2016
Posts: 572
GMAT 1: 750 Q49 V43
What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

Updated on: 13 Sep 2018, 02:52
1
LM wrote:
What is the sum of the multiples of 7 from 84 to 140, inclusive?

A. 896
B. 963
C. 1008
D, 1792
E. 2016

Lets use the simplest statistical concept:- Mean

$$Mean = \frac{Sum}{Total Terms}$$

$$Easy-way-to-find-mean-is= \frac{First + Last}{2}$$

$$\frac{84+140}{2} =\frac{224}{2} = 112$$

therefore $$112= \frac{SUM}{Total Terms}$$

$$Total-Terms-are \frac{(Last -First)}{Gap}+ 1$$

$$Total-Terms =\frac{140-84}{7} +1 = \frac{56}{7} + 1 = 8+1 = 9$$

$$112= \frac{SUM}{9}$$

SUM = 112*9 = 1008

ANSWER IS C
_________________

Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly.
FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.

Originally posted by LogicGuru1 on 05 Sep 2016, 23:39.
Last edited by LogicGuru1 on 13 Sep 2018, 02:52, edited 1 time in total.
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8656
Location: Pune, India
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

06 Sep 2016, 01:26
VeritasPrepKarishma wrote:
leonidbasin1 wrote:
I do not get the 4.5 part??

all you have to do on a quick test like gmat is this:

84, 91, 98, 105, 112, 119, 126, 133, 140.

i wouldn't even list 'em out on the test.

(84 + 140) / 4.5 = answer

Can someone please explain this?

This is incorrect.
The concept used is
Sum = Average * Number of elements

Average = (84+140)/2
Number of elements = 9

Sum = [(84+140)/2] * 9 = (84 + 140) * 4.5 = 1008

Also, check http://www.veritasprep.com/blog/2012/03 ... gressions/
It discusses the various Arithmetic Progression concepts.
_________________

[b]Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >

Director
Joined: 12 Nov 2016
Posts: 734
Location: United States
Schools: Yale '18
GMAT 1: 650 Q43 V37
GRE 1: Q157 V158
GPA: 2.66
Re: What is the sum of the multiples of 7 from 84 to 140, inclus  [#permalink]

### Show Tags

19 Jun 2017, 05:16
LM wrote:
What is the sum of the multiples of 7 from 84 to 140, inclusive?

A. 896
B. 963
C. 1008
D, 1792
E. 2016

We can apply an AP (Arithmetic Progression) formula for the sum of terms- this formula is applicable when a series of numbers is increasing by a fixed number (1 , 2 ,3 ...5 , 10 ,15.....120, 140, 160 etc). Where this formula wouldn't work is with a series of randomly increasing numbers such as 7, 11, 15. But anyways here is the formula

N= number of items in the series

n/2 (First term + Last term) = Sum of Series

there are 9 multiples of 7 between 84 and 140 so

9/2 (84 + 140) -

Thus

"D"
Re: What is the sum of the multiples of 7 from 84 to 140, inclus &nbs [#permalink] 19 Jun 2017, 05:16

Go to page    1   2    Next  [ 23 posts ]

Display posts from previous: Sort by

# What is the sum of the multiples of 7 from 84 to 140, inclus

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

 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®.