Calculating quartiles when the set is odd

[joyoftheheart]

I'm not clear on the procedure of finding quartiles when a number set has odd number of elements so that the median Q2 is also one of the elements.

Now, this element, Q2, is supposed to split the set into two halves, BUT, what about that number itself? Does it now belong to both of the subsets or to none? What is the convention ETS takes?

For a simplest example, let's say the set is: 1,2,3,4,5. Sure, Q2=3. But now do we have the further splitting like:
A: (123)(345) or
B: (12)(45)?

In the A case, Q1=2, Q3=4; in the B case: Q1=1.5, Q3=4.5. Which one is right?

[tommywallach]

It would be your second example (ignore the median).

-t