a maths question, page-49

And yet another way of looking at it:

You announce the draw.

What do you tell your employees?

That they have a 1 in 6 chance of drawing a black marble?

Of course! That's what they all have at the beginning. The fact that the chances change after each draw does not change their chances before the draw has occurred.

If the marbles are not revealed, it is impossible to determine the chances at each draw. All that is known is that each employee has a 1 in 6 chance of drawing a black. I would expect that this is assumed. If the marbles are revealed (bad idea IMO), why bother drawing any more at all once 5 have come out?