Two people walk into a room. After 30 minutes one leaves. How many people in the room and why?

30 because thirty people came in after

We don't know how many people were in the room before the two arrived, we don't know how many others arrived or left in the proceeding 30 minutes. We don't know if there's another method of a person not being in a room other than leaving (i.e. spontaneous human combustion, being dissolved in acid, ingestion, metamorphosis). In short, we can't comment with any authority on how many people are in the room.

Cant answer that not enough info and too many variables.

One, because of math.

I like all the answers that provided a figure or a way to get a figure. Very creative!

one less than how many were in the room when they walked in

One at least

16 plus 2 minus 1 , 17 , (oops I ment 17not 15 ) left in the room .. 15 mins later other one walks out ... how many are left ??

Are they siamese twins?