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heshamelaziry: Legendary Member; Posts: 869; Joined: Wed Aug 26, 2009 3:49 pmFollowed by: 3 members; Location: California; Thanked: 13 times

by heshamelaziry » Sun Nov 29, 2009 3:00 pm

Last September the total sales for a certain car dealership was 400% greater than the average monthly sales total for the other 11 months of the year. The sales total for September was approximately what percent of the year's sales ?

15%

27%

31%

42%

75%

OA C

Last edited by heshamelaziry on Sun Nov 29, 2009 8:58 pm, edited 1 time in total.

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Source: Beat The GMAT — Problem Solving | Sun Nov 29, 2009 3:00 pm

thephoenix: Legendary Member; Posts: 1560; Joined: Tue Nov 17, 2009 2:38 amFollowed by: 5 members; Thanked: 137 times

by thephoenix » Sun Nov 29, 2009 8:39 pm

imo c 31%

LET TOTAL SALE BE X FOR THE 11 MONTHS AVG SALES WILL BE X/11
SEPTEMBER SALES WILL BE 4X/11+X/11=5X/11

TOTAL YEARS SALES=X+5X/11=16X/11

sales total for September / YEARS SALES=(5X/11) /(16X/11)=APPROX 31%

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Mon Nov 30, 2009 12:01 am

thephoenix wrote:imo c 31%

LET TOTAL SALE BE X FOR THE 11 MONTHS AVG SALES WILL BE X/11
SEPTEMBER SALES WILL BE 4X/11+X/11=5X/11

TOTAL YEARS SALES=X+5X/11=16X/11

sales total for September / YEARS SALES=(5X/11) /(16X/11)=APPROX 31%

Good solution, but we could have simplified things a bit by ignoring the averages.

Just let every other month have sales of X and September have sales of 5X (as you did).

Then we simply take Sept/Year = 5X/(5X+11X) * 100% = 5/16 * 100% = (500/16)% which is a bit more than 30%.

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Gmatter2.0: Junior | Next Rank: 30 Posts; Posts: 29; Joined: Fri Oct 30, 2009 10:45 pm; Thanked: 1 times; GMAT Score:580

by Gmatter2.0 » Mon Nov 30, 2009 7:33 pm

VIC

Let the Sales per month for 11 months other than september be equal, and let the sale be 1000.
Sept Sales=400/100 *1000+1000=5000

Total Sales =11000+5000
=16000
Now 5000=x% * 16000

x=5/16 *100=31.25% ~= 31%

Answer is C.

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