# 2 probability questions

• Oct 20th 2008, 07:38 AM
Narek
2 probability questions
a lot of Thank you ...(Rofl)
• Oct 20th 2008, 07:44 AM
ddt
Quote:

Originally Posted by Narek
a lot of Thank you ...(Rofl)

As to the first: look at the probabilities of the complements:
P(U\E) = ???
P(U\F) = ???
and then look at P(U\(E n F)).

(where U is the "universe", i.e., all events).

As to the second: does it really matter which birthday person1 has? So, say it's January 13. Then look at the birthday of person2.
• Oct 20th 2008, 07:48 AM
tester85
Refer to the link below, you will be able to solve the 2nd problem.

Birthday problem - Wikipedia, the free encyclopedia
• Oct 20th 2008, 08:55 AM
Narek
cant solve the first one!!
I dont get the point .... can you solve it?(Thinking)
• Oct 20th 2008, 10:58 AM
ddt
Quote:

Originally Posted by Narek
I dont get the point .... can you solve it?(Thinking)

Try first: what's the probability that E does not occur, i.e. P(U \ E) ?
Likewise, the probability that F does not occur?

What's the sum of those?

What has that to do with the probability that (E n F) does not occur?
• Oct 20th 2008, 12:52 PM
Narek
answer to birthday problem
we dont know what day is for the first person, so we consider it as 1st january. and now we say, the probability of the second person having the same birthday is :

P= 1 / 366

__________________________________________________ ________

is this True???? thank you (Nod)
• Oct 20th 2008, 12:59 PM
ddt
Quote:

Originally Posted by Narek
we dont know what day is for the first person, so we consider it as 1st january. and now we say, the probability of the second person having the same birthday is :

P= 1 / 366

__________________________________________________ ________

is this True???? thank you (Nod)

Yes, that's correct.
• Oct 20th 2008, 02:48 PM
Narek
for the first one, no matter how hard I try, I dont understand the concept ... I need to see the solution, please (Wink)
• Oct 20th 2008, 08:44 PM
Narek
any suggestion???
any suggestion??? any guide? (Lipssealed)
• Oct 21st 2008, 01:09 AM
CaptainBlack
Quote:

Originally Posted by Narek
any suggestion??? any guide? (Lipssealed)

\$\displaystyle P(E\cup F)=P(E)+P(F)-P(E \cap F) \le 1\$

CB