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# MGMAT problem

Author Message
Intern
Joined: 11 Sep 2009
Posts: 18
Location: Tampa ,FL

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22 Sep 2009, 20:09
00:00

Difficulty:

(N/A)

Question Stats:

100% (00:16) correct 0% (00:00) wrong based on 12 sessions

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Sam earned a $2000 , commission on a big sale , raising his average commission by$100.If Sam's new average commission is \$900, how many sales has he made?

Ans:
a) 11
b) 12
c) 13

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Manager
Joined: 10 Aug 2009
Posts: 129

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22 Sep 2009, 20:24
1
This post was
BOOKMARKED
I think 12 sales (including the last one).

X represents the average prior to the last sale and N - the number of sales (NOT including the last sale)
x+100=900
x=800
sum of commissions fron N sales=800N

the average of total sales (oncluding the last one)= $$\frac{800N+2000}{N+1}=900$$
from here, N=11 and N+1=12
Senior Manager
Joined: 31 Aug 2009
Posts: 401
Location: Sydney, Australia

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22 Sep 2009, 23:51
2
KUDOS
Arrived at the same conclusion, slightly diff working but same thing.

Previous Average
1) Sum/N = 800

New Average
2) (Sum+2000) / (N+1) = 900

Subtract equations:
2)-1)
X+2000 = 900N+900
X = 800N
2000 = 100N+900
100N = 1100
N = 11

Manager
Joined: 15 Sep 2009
Posts: 119

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23 Sep 2009, 01:36
I wud go with option 12

800*x + 2000 = 900(x+1)
100x = 1100
x = 11
x+1 = 12
Senior Manager
Joined: 31 Aug 2009
Posts: 401
Location: Sydney, Australia

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23 Sep 2009, 02:03
Sorry, you are correct. Classic case of not reading question stem it is 12 not 11.
Intern
Joined: 11 Sep 2009
Posts: 18
Location: Tampa ,FL

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23 Sep 2009, 07:09
Yes , 12 is the right answer .
Manager
Joined: 27 Oct 2008
Posts: 181

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23 Sep 2009, 11:26
Soln:
New average is 900 for x + 1 items
Earlier average is 800 for x items

eq is
2000 + 800x = 900(x + 1)
solving for x
x = 11

Since the new total is (x + 1) therefore we have total of 12 items sold
Non-Human User
Joined: 09 Sep 2013
Posts: 6867

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21 Nov 2017, 10:31
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

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Re: MGMAT problem   [#permalink] 21 Nov 2017, 10:31
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# MGMAT problem

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