Question

A bag contains 20 checkers --10 red and 10 black. Find the probability of selecting 2 black checkers when they are chosen at random without replacement. Determine whether the event is dependent or independent.

Answer 1

For the first selection you have a 50% chance of picking a black marble.
For the second selection you will have 9 black marbles and 10 red marbles giving you a 45% chance of picking a black marble.
Multiply 50% by 45% and you get a 22.5% chance.

Two events are said to be independent if the result of the second event is not affected by the result of the first event.

Since the first marble is not replaced it affects the second selection which makes the event dependent.