Robin has a bag of 12 marbles. 8 are black and 4 are white. What is the chance that Robin will pick a white marble?

The chances are 4/12 = 1/3

The probability of choosing a marble from the bag is 1/1, sure to happen. The chance of picking a black marble out of the bag is 8/12, or 2/3. The probability that a white marble is chosen is 4/12, or 1/3. To find the probability of these two outcomes, there are a total of 12 marbles in the bag. If there are 4 white marbles, the chance that Robin can pick a white marble is 4 out of the 12 in the bag; the other 8 are black. For farther (and better) explination on probability, check out this link: http://www.mathsisfun.com/data/probability.html