The probability if you're drawing twice is the probability of getting the item on your first selection, or not getting the item on your first selection but then getting it on your second. That probability would be , where is the probability of not getting the item on any given selection.

If you're drawing 4 times, then the probability would be (i.e, getting it on your first selection, or not getting it on your first but then getting in on your second, or not getting it on your first two selection but then getting it on your third, or not getting it on your first three selections but then getting it on your fourth selection).

EDIT: Unless the probability of drawing the particular item doesn't remain constant for each selection.