## becca2212 4 years ago How to solve a probabilitiy when it has or in the problem. Like P (A or B)?

1. mathTalk

Just add the probaility if they are disjoint however take out P(A and B) if the sets are not disjoint.

2. becca2212

E.) was P (A and B) and then F.) is P (A or B). Earlier in the question I did P(A)=230/580 and P(B)=200/580. What should I do to find P (A or B)

3. mathTalk

P(A or B) =1-P'(AorB) =1- 150/580=430/580

4. becca2212

I am sorry where did you get the 150 at?

5. mathTalk

total P = P(A)+p(B)+P'(A or B)

6. mathTalk

=1

7. becca2212

So if I need to solve for P (B or D) and P (B) was 200/580 and P (D) was 250/580. How do I solve this one?

8. mathTalk

450/580

9. becca2212

Why would the problems be so different? Why did I use 1- in the first one but the second one just added the top numbers?

10. mathTalk

I was wrong

11. mathTalk

P(A+B)= P(A)+P(B)-p(aandB)

12. becca2212

I know you gave me the formula but I dont understand how you got 150 still.

13. mathTalk

sorry for confusing you. I was wrong there.

14. becca2212

haha its ok I just dont get probability at all. So can we start over real quick. I need to find P (A or B). P (A) was 230/580 and P(B) was 200/580.

15. mathTalk

simply add the two probabilities ?

16. mathTalk

but i am not sure about the intersection.