Official Solution: A campus bookstore bought 60 notebooks for a total of 540 euros. All of the notebooks were sold during a three-week orientation period. The notebooks were sold for 14 euros each in week 1, 11 euros each in week 2, and 8 euros each in week 3. Was the number of notebooks sold in week 1 greater than the number sold in week 3? (1) Fewer than 20 notebooks were sold in week 2.
We know:
\(\{week\ 1\} + \{week\ 2\} + \{week\ 3\} = 60\)
But this statement gives information only about \(\{week\ 2\}\). It still leaves many possible values for \(\{week\ 1\}\) and \(\{week\ 3\}\).
Not sufficient.
(2) The bookstore’s total profit on the notebooks was less than 120 euros.
The total cost was 540 euros, so the total revenue was less than \(540 + 120 = 660\) euros.
Thus, the average selling price was less than \(\frac{660}{60} = 11\) euros.
Now 11 euros is exactly the price in week 2, and it is exactly halfway between 14 euros in week 1 and 8 euros in week 3.
So, if the overall average selling price is less than 11 euros, then more notebooks must have been sold at 8 euros than at 14 euros, because only then would the average be pulled below 11 euros. Therefore,
\(\{the\ number\ of\ notebooks\ sold\ in\ week\ 3\ at\ 8\ euros\} > \{the\ number\ of\ notebooks\ sold\ in\ week\ 1\ at\ 14\ euros\}\)
So the answer to the question is No. Sufficient.
Answer: B