simple average

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magical cook: Master | Next Rank: 500 Posts; Posts: 484; Joined: Sun Jul 30, 2006 7:01 pmFollowed by: 1 member; Thanked: 2 times

by magical cook » Mon Jan 28, 2008 2:00 pm

Last year Bakery A had total sales of cookies in December that was 4 times the average (arithmetic mean) of the monthly cookie sales totals for January through June and 3 times the average total cookie sales for July through November. The cookie sales total for December was what fraction of the total cookie sales for the year?

(A) 3/14
(B) 6/25
(C) 1/4
(D) 2/3
(E) 12/19

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Source: Beat The GMAT — Problem Solving | Mon Jan 28, 2008 2:00 pm

cris: Master | Next Rank: 500 Posts; Posts: 128; Joined: Sat Nov 17, 2007 11:59 am; Thanked: 1 times

by cris » Mon Jan 28, 2008 2:51 pm

mmmm not sure, B??

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camitava: Legendary Member; Posts: 645; Joined: Wed Sep 05, 2007 4:37 amFollowed by: 5 members; Location: India; Thanked: 34 times

by camitava » Mon Jan 28, 2008 8:32 pm

Agree with, Cris! It should be - 6/25 i.e. B.
Dec : Cookies sold = 12x (Say)
Jan - Jun: Cookies sold = avg cookies sold * no of months = 3x * 6 = 18x
Jul-Nov: Cookies sold = avg cookies sold * no of months = 4x * 5 = 20x
So fraction = 12x/(12x + 18x + 20x) = 6/25
Magical Cook, what's the OA?

Correct me If I am wrong

Regards,

Amitava

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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 Jan 28, 2008 9:37 pm

camitava wrote:Agree with, Cris! It should be - 6/25 i.e. B.
Dec : Cookies sold = 12x (Say)
Jan - Jun: Cookies sold = avg cookies sold * no of months = 3x * 6 = 18x
Jul-Nov: Cookies sold = avg cookies sold * no of months = 4x * 5 = 20x
So fraction = 12x/(12x + 18x + 20x) = 6/25
Magical Cook, what's the OA?

Correct!

We can make life even a bit easier by forgetting about the "x".

Let's pick 12 for December cookie sales (since that's the lowest common multiple of 3 and 4, the other numbers involved).

In that case, each of Jan-June will average 3 cookies and each of July-Nov will average 4 cookies.

So, we have 6*3 + 5*4 + 12 = 18+20+12 = 50 total cookies

December is 12/50 or 6/25 of the whole year.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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sibbineni: Master | Next Rank: 500 Posts; Posts: 222; Joined: Fri Jan 04, 2008 8:10 pm; Thanked: 15 times

by sibbineni » Tue Jan 29, 2008 3:43 am

Hi stuart,

Jan - Jun: Cookies sold = avg cookies sold * no of months = 3 * 6 = 18 i was thinking 4*6 as mentioned in the question

Jul-Nov: Cookies sold = avg cookies sold * no of months = 4* 5 = 20 i was thinking 5*3 as mentioned in the question

can you please explain the answer.

Thanks,
Sibbineni

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camitava: Legendary Member; Posts: 645; Joined: Wed Sep 05, 2007 4:37 amFollowed by: 5 members; Location: India; Thanked: 34 times

by camitava » Tue Jan 29, 2008 4:29 am

sibbineni wrote:Hi stuart,

Jan - Jun: Cookies sold = avg cookies sold * no of months = 3 * 6 = 18 i was thinking 4*6 as mentioned in the question

Jul-Nov: Cookies sold = avg cookies sold * no of months = 4* 5 = 20 i was thinking 5*3 as mentioned in the question

can you please explain the answer.

Thanks,
Sibbineni

sibbineni, why it will be 4 * 6 and 3 * 5 for Jan - Jun & Jul-Nov respectively? The Qs is saying -

total sales of cookies in December that was 4 times the average (arithmetic mean) of the monthly cookie sales totals for January through June and 3 times the average total cookie sales for July through November

So if in december, no of cookies = 12x
so jan-Jun: 4k = 12x -> k = 3x -> so avg is 3x or 3 (according to Stuart!)

Got me?

Correct me If I am wrong

Regards,

Amitava

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magical cook: Master | Next Rank: 500 Posts; Posts: 484; Joined: Sun Jul 30, 2006 7:01 pmFollowed by: 1 member; Thanked: 2 times

by magical cook » Tue Jan 29, 2008 9:47 am

thanks - answer is b.

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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 » Tue Jan 29, 2008 10:34 am

sibbineni wrote:Hi stuart,

Jan - Jun: Cookies sold = avg cookies sold * no of months = 3 * 6 = 18 i was thinking 4*6 as mentioned in the question

Jul-Nov: Cookies sold = avg cookies sold * no of months = 4* 5 = 20 i was thinking 5*3 as mentioned in the question

can you please explain the answer.

Thanks,
Sibbineni

According to the question stem, December was 4 times the average for Jan-June. So, if we let December = 12, we get:

12 = 4 * Jan-June
Jan-June = 12/4 = 3

Similarly, for July-Nov, if December is 3 times the average for July-Nov, we get:

12 = 3 * July-Nov
July-Nov = 12/3 = 4

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sibbineni: Master | Next Rank: 500 Posts; Posts: 222; Joined: Fri Jan 04, 2008 8:10 pm; Thanked: 15 times

by sibbineni » Tue Jan 29, 2008 3:42 pm

Thanks Stuart

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sibbineni: Master | Next Rank: 500 Posts; Posts: 222; Joined: Fri Jan 04, 2008 8:10 pm; Thanked: 15 times

by sibbineni » Tue Jan 29, 2008 3:43 pm

Thanks Stuart

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