Suppose we pick 2 balls out of a box without
replacement.
Let's say 3
are red
and 5
are blue.
What is the probability of picking a
red ball then a blue
ball?
|
Solve |
Step |
| Pick red first. Pr(red) = 3/8 |
There are a total of 8 balls in the box. |
|
Then pick blue. Pr(blue) = 5/7 |
Notice it is not 5/8 since once we picked a red ball there is one less ball in the box. |
|
Pr(red then blue) = 3/8 × 5/7 = 15/56 |
These events are not independent. |