Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

I'm dealing with a problem in probability, there's:

Let P be an probability function in $\Omega{\{a1, a2, a3\}}$, find $P(a1)$ whether:

$P(a2) = \dfrac{1}{3}$ and $P(a3) = \dfrac{1}{4}$

I don't even know from where to start, since I'm a beginner in probability;

Thanks in advance;

share|improve this question
1  
Do you mean ‘find $P(a1)$ if $P(a2)=\frac13$ and $P(a3)=\frac14$’? If so, use the fact that $P(a1)+P(a2)+P(a3)=1$: the probabilities of the individual outcomes must add up to $1$. –  Brian M. Scott Apr 11 '12 at 1:24
2  
Three things: this would look a lot better if you tex it, you should go back and accept answers to your previous questions (you'll get more help if you do), and as a hint, what is $P(\Omega)$? Using that $\Omega - (\{a_2\}\cup\{a_3\}) = \{a_1\}$ what does that tell you? –  Chris Janjigian Apr 11 '12 at 1:25

1 Answer 1

up vote 2 down vote accepted

Hint

  1. $P(\{a_1,a_2,a_3\})=1$
  2. $P(A \cup B)=P(A)+P(B)$ whenever $A \cap B =\varnothing$.
share|improve this answer
    
Thanks everybody, I now I've noticed that the sum of events is equal 1, thanks; –  aajjbb Apr 11 '12 at 2:51
1  
@aajjbb then please accept the solution (and solutions to your previous problems) –  Chris Janjigian Apr 11 '12 at 3:08
    
Do you know about accepting answers to your questions? Do you understand why it's considered a good idea to do so? Please go through the faq if you are unsure. –  Gerry Myerson Apr 11 '12 at 4:21

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.