if there are 4 dismonds on the board?

[qcnb]

13 Diamonds in a deck, minus 4 on the table, equals 9 outs.
9 outs out of 52 cards in a deck, Minus the 7 cards that are already seen by you ( 5 on table, 2 Hole )
9/45 = 20%

So basically, about 1/5

All this is assuming you do not hold one in your hands as well.

Edit : As posted while I was posting is right ! I forgot to double up considering he has 2 cards.

40% is right.