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Wordy Data Sufficiency

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by Apl28 » Tue Dec 02, 2008 8:22 pm
Store S sold a total of 90 copies of a certain book during the seven days last week and it sold different numbers of copies on any 2 days. If for the seven days Store S sold the greatest number of copies on Saturday and the second greatest number of copies on Firday, did Store S sell more than 11 copies on Friday?

1) Last week Store S sold 8 copies on Thursday
2) Last week Store S sold 38 copies on Saturday

[spoiler]B
[/spoiler]
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Source: — Data Sufficiency |

by anayeri » Tue Dec 02, 2008 8:49 pm
Statement 1)

We want to use this statement to see if on the minimum, Friday sold 12+ copies. Let's assume Thursday was the third highest day, could Friday have sold less than 12 copies? Let's see:

Su Mo Tu We Th Fr(++)
4 5 6 7 8 11, so this would make Saturday 49 to get to 90, so yes, Friday COULD have sold let's than 12 copies. So insufficient.

Statement 2)

We know that the higest day (Saturday) sold 38 copies. Given that, can we prove that the second highest day (friday) had less than 12 copies sold, while maximizing the other days? Let's see:

Su Mo Tu We Th Fr(++) Sa(+)
6 7 8 9 10 11 38

The sum of these numbers (89) falls 1 short of 90 - so, Friday must have sold atleast 12 copies.

Answer B.
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by missrochelle » Sat Aug 28, 2010 3:42 pm
in this question...how are we "proving" that more than 11 copies were sold by setting friday equal to 11 and testing whether they sold "less than 12". i dont understand the wording....
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by kevincanspain » Mon Aug 30, 2010 12:20 am
missrochelle wrote:in this question...how are we "proving" that more than 11 copies were sold by setting friday equal to 11 and testing whether they sold "less than 12". i dont understand the wording....
Good question!

It is apparent from (2) that more than 11 copies could have been sold on Friday (it may be that few copies were sold during the rest of the week). The question is "Must it be true that more than 11 were sold on Friday?"

We can answer this question by seeing whether it is possible that exactly 11 were sold on Friday. We find out that if exactly 11 were sold on Friday, at most 89 were sold during the week, not 90 as stated in the text.

Thus the possibility that the answer to the question is no is inconsistent with the facts given, meaning that the answer must be yes.
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