The odds will change each time a marble is chosen.
At the start you have a one in 5 chance of drawing a black marble.
If a white marble is chosen first then you then have a 5 in 29 chance of drawing a black marble.
If a black marble is chosen first then you have a 4 in 29 chance of drawing a black marble. the chances are determined by the number of black and white marbels left that make up the population of marbles.
Best to pick when you get to chose based on the relative odds.
