To give an example. if one has a bag of 5 blue marbles and five red marbles, the probability of drawing a blue marbLe on the first draw is 5/10 or 1/2.
On the second draw, if the first marble was blue then in the bag there are 4 blue marbles and 5 red marbles and the ptobabilty of drawing a blue marble on the second draw is 4/9.
If on the first draw the marble pulled of was red then in the bag there are 5 blue marbles and 4 red marbles left over. So, in this case the probability of getting a blue marble is 5/9.
Even A is independent but even t B is dependent on event A.