**Problem statement**

Set N consists of the first 9 positive multiples of 3

Quantity A - The average of the first and last terms in the set

Quantity B - The average of the third and seventh terms in the set

**Solution from 5 lb:**

C

**Question:**

For the solution to be C, one must assume that the set is ordered ascending or descending. But this isn’t explicitly specified. So the answer is either D or I am not interpting the question correctly. I find it ambiguous. Why must one assume this is an ordered set?