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# During the first 11 months of a recent year, a certain charitable orga

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Joined: 26 Jul 2014
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During the first 11 months of a recent year, a certain charitable orga  [#permalink]

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27 Jul 2014, 11:22
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89% (00:53) correct 11% (00:58) wrong based on 314 sessions

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During the first 11 months of a recent year, a certain charitable organization received an average of $20,600 per month in donations. How much did the organization receive in donations during December of that year if the average amount of donations per month for the entire year was$21,000?

A. $21,400 B.$21,600
C. $24,000 D.$25,400
E. $25,800 ##### Most Helpful Expert Reply Math Expert Joined: 02 Sep 2009 Posts: 48074 Re: During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 27 Jul 2014, 14:32 9 6 eleuth wrote: During the first 11 months of a recent year, a certain charitable organization received an average of$20,600 per month in donations. How much did the organization receive in donations during December of that year if the average amount of donations per month for the entire year was $21,000? A.$21,400
B. $21,600 C.$24,000
D. $25,400 E.$25,800

The average to rise by $400, from$20,600 to $21,000, December donation should compensate those$400 for each of the first 11 months, so should have 11*400 more than $21,000: 11*400 + 21,000 =$25,400.

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Re: During the first 11 months of a recent year, a certain charitable orga  [#permalink]

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27 Jul 2014, 12:31
1
1
Say for December month, It is X

then
$$11*(20600) + X = 12 * (21000)$$
=> x = 25400 - Option D
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Intern
Joined: 13 Jul 2014
Posts: 10
Location: India
Concentration: Operations, Technology
GMAT Date: 11-06-2014
GRE 1: Q159 V144
Re: During the first 11 months of a recent year, a certain charitable orga  [#permalink]

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20 Oct 2014, 18:08
eleuth wrote:
During the first 11 months of a recent year, a certain charitable organization received an average of $20,600 per month in donations. How much did the organization receive in donations during December of that year if the average amount of donations per month for the entire year was$21,000?

A. $21,400 B.$21,600
C. $24,000 D.$25,400
E. $25,800 Hello There, Average for 11 months = 20,600 M1 + M2 + ……. + M11 ------------------------------- = 20,600 11 M1 + M2 +……..+ M11 = 20,600 X 11 = 2,26,600 Average for 12 months = 21,000 M1 + M2 + ……. + M11 + M12 ----------------------------------------- = 21,000 12 (M1 + M2 +……..+ M11) + M12 = 21,000 X 12 2,26,600 + M12 = 2,52,000 M12 = 2,52,000 – 2,26,600 = 25,400 _________________ Regards, Bharat Bhushan Sunkara. "You need to sacrifice what you are TODAY, for what you want to be TOMORROW!!" Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 8199 Location: Pune, India Re: During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 20 Oct 2014, 20:31 bharatS wrote: eleuth wrote: During the first 11 months of a recent year, a certain charitable organization received an average of$20,600 per month in donations. How much did the organization receive in donations during December of that year if the average amount of donations per month for the entire year was $21,000? A.$21,400
B. $21,600 C.$24,000
D. $25,400 E.$25,800

Hello There,
Average for 11 months = 20,600
M1 + M2 + ……. + M11
------------------------------- = 20,600
11

M1 + M2 +……..+ M11 = 20,600 X 11 = 2,26,600

Average for 12 months = 21,000
M1 + M2 + ……. + M11 + M12
----------------------------------------- = 21,000
12

(M1 + M2 +……..+ M11) + M12 = 21,000 X 12
2,26,600 + M12 = 2,52,000
M12 = 2,52,000 – 2,26,600 = 25,400

Your method is correct but it involves quite a bit of calculations. The method used by Bunuel above is much more crisp. This method is discussed in detail here: http://www.veritasprep.com/blog/2012/04 ... etic-mean/
Check it out.
_________________

Karishma
Veritas Prep GMAT Instructor

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Intern
Joined: 13 Jul 2014
Posts: 10
Location: India
Concentration: Operations, Technology
GMAT Date: 11-06-2014
GRE 1: Q159 V144
Re: During the first 11 months of a recent year, a certain charitable orga  [#permalink]

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20 Oct 2014, 21:54
VeritasPrepKarishma wrote:
bharatS wrote:
eleuth wrote:
During the first 11 months of a recent year, a certain charitable organization received an average of $20,600 per month in donations. How much did the organization receive in donations during December of that year if the average amount of donations per month for the entire year was$21,000?

A. $21,400 B.$21,600
C. $24,000 D.$25,400
E. $25,800 Hello There, Average for 11 months = 20,600 M1 + M2 + ……. + M11 ------------------------------- = 20,600 11 M1 + M2 +……..+ M11 = 20,600 X 11 = 2,26,600 Average for 12 months = 21,000 M1 + M2 + ……. + M11 + M12 ----------------------------------------- = 21,000 12 (M1 + M2 +……..+ M11) + M12 = 21,000 X 12 2,26,600 + M12 = 2,52,000 M12 = 2,52,000 – 2,26,600 = 25,400 Your method is correct but it involves quite a bit of calculations. The method used by Bunuel above is much more crisp. This method is discussed in detail here: http://www.veritasprep.com/blog/2012/04 ... etic-mean/ Check it out. Hello There, Ya, was just trying to explain the concept. Surely will follow Bunuel. Thanks for your inputs. _________________ Regards, Bharat Bhushan Sunkara. "You need to sacrifice what you are TODAY, for what you want to be TOMORROW!!" Senior Manager Status: Math is psycho-logical Joined: 07 Apr 2014 Posts: 421 Location: Netherlands GMAT Date: 02-11-2015 WE: Psychology and Counseling (Other) Re: During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 15 Jan 2015, 10:18 While I like the response by MKS, I also tried to do it another way and it doesn't work out. Could you tell me what I am doing wrong? So, starting by looking for the sum of the earning we have: 20600 = S/11 --> S = 226600 Then if we add the remaining earning for the last month of the year this becomes: 21000 = (226600 + x) / 12 => x = 229400, which is wrong... EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 12217 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 15 Jan 2015, 22:29 Hi pacifist85, Your set-up and logic are fine. When you get to this point in the "math".... 21000 = (226600 + x) / 12 ....What did you do next? (you include a value for X that was incorrect, so I don't know HOW you worked through your math). Here is a correct series of math "steps": 21,000(12) = 252,000 252,000 = 226,600 + X 25,400 = X Final Answer: 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
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Senior Manager
Status: Math is psycho-logical
Joined: 07 Apr 2014
Posts: 421
Location: Netherlands
GMAT Date: 02-11-2015
WE: Psychology and Counseling (Other)
Re: During the first 11 months of a recent year, a certain charitable orga  [#permalink]

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16 Jan 2015, 01:18
Hi Rich,

What I did next was to just solve for X:
21000 = (226600 + x) / 12 => x = 229400.

So, my reasoning behind this was to add the missing amount to the S ( 226600 + x ) and divide again by 12, because now we have a new day to account for ( / 12 ). And I know see that I actually get the correct answer. As 21000*12=226600+x --> 252000 = 226600 + x --> 252000 - 226600 = x --> x = 25400.

At the moment I don't know what my problem was.. Perhaps I shouldn't be GMATing for 12 hours evryday...

But, what did you mean with "What did you do next? (you include a value for X that was incorrect, so I don't know HOW you worked through your math)". Why was adding X there incorrect?

Thank you!
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 12217
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: During the first 11 months of a recent year, a certain charitable orga  [#permalink]

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16 Jan 2015, 12:16
Hi pacifist85,

I was asking about how you did your calculation because you did not include that information. There was just a number (229,400) and a comment stating "...which is wrong." You got to that number somehow, but you did not explain how.

Just about every Test Taker makes some silly mistakes during practice; to keep those silly mistakes from happening AGAIN, it's important to define WHY they happened in the first place. Maybe you didn't take enough notes, maybe you did math in your head, maybe you used "math rules" incorrectly. Whatever the reason, by defining it....you should be able to fix it.

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!*********************** Senior Manager Status: Math is psycho-logical Joined: 07 Apr 2014 Posts: 421 Location: Netherlands GMAT Date: 02-11-2015 WE: Psychology and Counseling (Other) Re: During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 17 Jan 2015, 02:07 Thank you Rich. It is true that I make such silly mistakes more often than I should. Be it in mistakes is easy calculations or even copying the figures incorrectly... Not sure what is wrong there. I guess I cannot focus as much as needed! Thank you though, because up until you told me that the solution seems correct (apart from the result of course) I was thinking that I was solving the problem incorrectly. Which was surprising since statistics is one of my strengths! Intern Joined: 23 Sep 2014 Posts: 36 Location: India Concentration: Marketing, Finance GMAT 1: 670 Q48 V34 During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 01 Dec 2016, 08:06 Hi Bunuel VeritasPrepKarishma, I was reviewing the GMATPrep mock I gave today, I scored a Q48 with 7 incorrect, with last 17 Q's correct. This particular question came as Q28( The difficulty level mentioned here is sub 600), and Q27 that came in the mock has a difficulty level of 700+ on GMAT Club, are the GMAT prep test not adaptive? or is the same fluctuation in the difficulty level of the Q can be expected in the Exam? I am a retaker, have Q46 and Q44 in my previous two attempts, so needed to be sure, whether this is an inflated score or pretty much according to my current ability. Exam Pack 1 : GMAT3 (Q48,V37) GMAT4(Q48,V39) TIA Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 8199 Location: Pune, India Re: During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 02 Dec 2016, 20:54 1 believer700 wrote: Hi Bunuel VeritasPrepKarishma, I was reviewing the GMATPrep mock I gave today, I scored a Q48 with 7 incorrect, with last 17 Q's correct. This particular question came as Q28( The difficulty level mentioned here is sub 600), and Q27 that came in the mock has a difficulty level of 700+ on GMAT Club, are the GMAT prep test not adaptive? or is the same fluctuation in the difficulty level of the Q can be expected in the Exam? I am a retaker, have Q46 and Q44 in my previous two attempts, so needed to be sure, whether this is an inflated score or pretty much according to my current ability. Exam Pack 1 : GMAT3 (Q48,V37) GMAT4(Q48,V39) TIA GMAT Prep is adaptive. Some sudden variation in difficulty level could be there because the algorithm considers various aspects (other than the difficulty level) such as the topics that still need to be tested, the question format to be given etc while selecting the next question. There is no reason for the score to be inflated. _________________ 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 > GMAT self-study has never been more personalized or more fun. Try ORION Free! Intern Joined: 23 Sep 2014 Posts: 36 Location: India Concentration: Marketing, Finance GMAT 1: 670 Q48 V34 Re: During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 02 Dec 2016, 21:21 VeritasPrepKarishma wrote: believer700 wrote: Hi Bunuel VeritasPrepKarishma, I was reviewing the GMATPrep mock I gave today, I scored a Q48 with 7 incorrect, with last 17 Q's correct. This particular question came as Q28( The difficulty level mentioned here is sub 600), and Q27 that came in the mock has a difficulty level of 700+ on GMAT Club, are the GMAT prep test not adaptive? or is the same fluctuation in the difficulty level of the Q can be expected in the Exam? I am a retaker, have Q46 and Q44 in my previous two attempts, so needed to be sure, whether this is an inflated score or pretty much according to my current ability. Exam Pack 1 : GMAT3 (Q48,V37) GMAT4(Q48,V39) TIA GMAT Prep is adaptive. Some sudden variation in difficulty level could be there because the algorithm considers various aspects (other than the difficulty level) such as the topics that still need to be tested, the question format to be given etc while selecting the next question. There is no reason for the score to be inflated. This helps a lot. Many thanks Manager Joined: 26 Mar 2017 Posts: 145 Re: During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 15 Jun 2017, 11:59 MKS wrote: Say for December month, It is X then $$11*(20600) + X = 12 * (21000)$$ => x = 25400 - Option D well I spent way too much time trying to find a way avoiding the long multiplication _________________ I hate long and complicated explanations! Intern Joined: 18 Jan 2017 Posts: 40 Re: During the first 11 months of a recent year, a certain charitable orga [#permalink] ### Show Tags 11 Dec 2017, 17:43 jadon wrote: During the first 11 months of a recent year, a certain charitable organization received an average of$20,600 per month in donations. How much did the organization receive in donations during December of that year if the average amount of donations per month for the entire year was $21,000? A.$21,400
B. $21,600 C.$24,000
D. $25,400 E.$25,800

average for 11 months = 20,600
20,600= x/11
x=226,600

average for the year= 21,000
21,000=x/12
x=252,000

252,000-226,600= 25,400
Re: During the first 11 months of a recent year, a certain charitable orga &nbs [#permalink] 11 Dec 2017, 17:43
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