3/28 exactly, or approximately 10.7%
Since we're drawing without replacement, let's first calculate the probability that the 1st marble is white. There are 3 white marbles out of a total of 8 marbles. So the probability of the 1st marble being white is 3/8.
Now assuming that the first marble picked is white, the probability of the second marble is 2 out of the 7 remaining marbles. So it's probability is 2/7.
This means that the probability of both marbles being white is 3/8 * 2/7 = 6/56 = 3/28, or approximately 10.7%
