At first, there are a total of 17 marbles in the bag.
The probability of pulling out the first red marble = 6/17.
The probability of pulling out the second red marble = (6-1)/(17-1) = 5/16
The probability of pulling out the third red marble = (5-1)/(16-1) = 4/15
Because we need these 3 events to happen consecutively, the probability of it happening = 6/17 x 5/16 x 4/15 = 0.029% (nearest thousandth).