How do u proof these?

1. Aug 23, 2004

Altemicione

1. Prove each of the following statements (assume that any conditioning event has positive probability).
(a) If A is subset of B then P(B|A)=1 and p(A|B)=P(A)/P(B).
(b) If A and B are mutually exclusive, then p(A|A u B)=((P(A)/((P(A)+P
(B))
(C) P(A n B n C)= P(A|B n C) P( B|C) P(C)

I"m really having problem in doing these. could someone help me out?

2. Aug 23, 2004

matt grime

You just need to use the rules/identities of probability:

P(X|Y) = P(XnY)/P(Y)

and if A < B, then P(AnB)= P(A) since AnB=A, and P(AuB)=P(B) since AuB=B

if A and B are mutually exclusive then P(AnB)=0 and P(AuB)=P(A)+P(B)

the third follows from repeatedly applying the formula for conditional probability.

3. Aug 23, 2004

Wong

Moderator's note: please don't do others' homework for them

Last edited by a moderator: Aug 23, 2004
4. Aug 23, 2004

Hurkyl

Staff Emeritus
Have you been able to get anywhere on this, Altemicione?

5. Aug 30, 2004

supundika

Moderator's note: Same goes for you

Last edited by a moderator: Aug 30, 2004
6. Aug 30, 2004

Jin314159

Why can't we help a brother out?

7. Aug 31, 2004

matt grime

you can, but just feeding the answers helps no one.

8. Aug 31, 2004

Tom McCurdy

helps him pass his class
so it helps one person
then it helps his parents so they have to pay less for when he goes to college if he is still in high school
so then the fincacial benefits spread through is family
so in the end it could help a lot of people

plus he prob learn how to do in class tomorrow
but if u dont' have hw u get 0

9. Sep 1, 2004

Gokul43201

Staff Emeritus
You think feeding him homework solutions makes him a better student and improves his odds of scoring higher in SATs (or whatever) ?

10. Sep 1, 2004

humanino

"If someone is hungry, don't give him a fish : teach him to fish !"
who said that ?

11. Sep 2, 2004

matt grime

Probably Gandhi

12. Sep 2, 2004

HallsofIvy

Staff Emeritus
"If you give a man a fish, he will eat for a day. If you teach a man to fish, he will never work another day in his life!"

13. Sep 2, 2004

Galileo

Or:

If you give a man a fish he will eat for a day. If you teach a man to fish he will drink beer, tell lies and wear a stupid hat.

14. Sep 2, 2004

humanino

Thanks you all for answering my "off-topic" question ! (although Galileo's version looks suspicous to me (^_^)

15. Sep 2, 2004

Gokul43201

Staff Emeritus
You mean 'fishy' ?

16. Sep 2, 2004

humanino

Sorry, I am not too sure about what fishy could mean ...