We’re back with the next installment in an occasional series on the Veritas Prep Blog, called “GMAT Gurus Speak Out.” Veritas Prep has dozens of experienced GMAT instructors around the world (all of whom have scored in the 99th percentile on the GMAT), and it’s amazing how much collective experience they have in preparing students for the exam. This new series brings some of their best insights to you. Our latest tip comes courtesy of John Chismody, a Veritas Prep GMAT instructor in Pittsburgh.

Let’s dig into a GMAT Data Sufficiency problem:

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

(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.

Unlike most quantitative GMAT problems, this particular data sufficiency question is not asking for a fixed value, but whether Store S sold more than a certain number of books on Friday. The stimulus does not provide specific values. All that one knows is that the greatest and second greatest volume of sales was on Saturday and Friday, respectively, and that the store sold a different number of books on each of the 7 days:

Friday: 2nd greatest day
Saturday: greatest day

Because the problem is open-ended, do not waste time trying to make deductions because none can be made. Move to the two statements.

Statement (1) by itself is not helpful. Knowing 8 copies on Thursday tells one nothing about Friday’s sales, which could have more or less than 11 copies sold.
However, statement (2) is relevant because it provides specific information on the day that sold the greatest number of copies. Think logically. Since the question asked whether Store S sold more than 11 copies on Friday, assume that it sold only 11 copies on this day:

Friday: 11 copies
Saturday: 38 copies

That is a total of 49 copies sold on Friday and Saturday. Since the total copies for the week is 90, then the store needs to sell 41 books (90 – 49) for the remaining five days. Assume it sold the greatest number of books on each of the days, but remember that the store sold a different number of copies on each of these days:

Sunday: 6
Monday: 7
Tuesday: 8
Wednesday: 9
Thursday: 10
Friday: 11
Saturday: 38

That only gives the store 40 copies maximum it could sell on Sunday through Friday, making the total for the week 89, which is less than the 90 copies that the store sold. Thus, the store had to sell more than 11 copies on Friday. Statement (2) alone is therefore sufficient, making the correct response (B).

This problem is not difficult, but different from most quantitative questions. Be alert when a problem gives such phrases as: the greatest, the least, more than, less than. In such cases, think holistically and not strictly in finite terms.

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