christinee wrote:

Please show how to solve this data sufficiency problem and share any tips for tackling problems of this nature:

Store S sold a total of 90 copies of a certain book during the 7 days of last week, and it sold different numbers of copies on any two of the days. If for the 7 days Store S sold the greatest number of copies on Saturday and the 2nd greatest number of copies on Friday, did Store S sell more than 11 copies on Fri?

1)Last week Store S sold 8 copies of the book on Thursday

2) Last week Store S sold 38 copies of the book on Saturday

Thanks in advance

B.

1) Here we cannot say whether >11 copies were sold on Friday because we don't know whether 8 is the highest number of copies sold on S,M,T,W,Thurs . If it is the highest , then number of copies on Friday can be 9,10,11,12,.. Also, if on Monday 12 copies were sold then Friday will be 13,14,...We cant say anything about Friday.

INSUFF

2) Lets assume that on Friday 11 copies are sold. This has the following implications:

=> Numbers sold on S,M,T,W,Thurs will be <11 and different. For eg. 1,2,3,4,5 OR 6,7,8,9,10.

Lets take the possibility of highest number of books on S,M,T,W,Thurs ie. 6,7,8,9,10. Note that this is the BEST case.

=> 40 books are sold upto Thursday

Total books sold = 40 + 11(our assumption) + 38 = 89. ( which is 1 less than 90 )

Hence, number of books sold on Friday MUST be > 11.

SUFF