# Thread: Probability homework help again...

1. ## Probability homework help again...

I'm very stuck here as I do not know how to add independant events! Here is the question:

P(A) = 13/25
P(B) = 9/25
P(A|B)= 5/9

Determine the probabilties...

a) P(A or B or Both)
b) P(A'|B')
c) P(A occurs or B does not occur)

What is the best way of tackling these problems?

Thanks guys!

2. Hello, anthmoo!

Given: .P(A) = 13/25, .P(B) = 9/25, .P(A|B)= 5/9

Determine the probabilties:.

a) P(A U B) . . b) P(A'|B') . . c) P(A U B')

I would use Bayes' Theorem, then draw a Venn diagram.

. . . . . . . . . . . . . . . P(A ∩ B)
We have: .P(A|B) .= .---------- .= .5/9
. . . . . . . . . . . . . . . . . P(B)

. . . . . . . . . . . . . . . . . . . . .P( A ∩ B)
Since P(B) = 9/25, we have: .----------- .= .5/9
. . . . . . . . . . . . . . . . . . . . . .9/25

. . Hence: .P(A ∩ B) .= .1/5

Now we can draw the Venn diagram.

Code:
      *---------------------------------------------------*
|                                                   |
|                   *-----------------------*       |
|                   |                     A |       |
|                   |           8/25        |       |
|                   |                       |       |
|       *-----------+-----------*           |       |
|       |           |           |           |       |
|       |           |    1/5    |           |       |
|       |           |           |           |       |
|       |           *-----------*-----------*       |
|       |                       |                   |
|       |      4/25             |                   |
|       | B                     |                   |
|       *-----------------------*         8/25      |
|                                                   |
*---------------------------------------------------*
You should be able to answer the questions now.

3. Originally Posted by Soroban
Hello, anthmoo!

I would use Bayes' Theorem, then draw a Venn diagram.

We haven't covered either of those =/ or anything with ∩ in..

Is there any other way to do it?

Is ∩ the same as | ? P(A|B) being the probability of A given that B has already occured.