# Help with proving probability equations

• Oct 11th 2012, 01:06 PM
jennyk
Help with proving probability equations
Hey, if anyone has time to give me some guidance on how to prove these i would be so grateful (Rock) thank you... :

i) P(A∩B) ≥ P(A) +P(B)−1,
ii) P(A∆B) = P(A) +P(B)−2P(A∩B)
• Oct 11th 2012, 01:28 PM
Plato
Re: Help with proving probability equations
Quote:

Originally Posted by jennyk
i) P(A∩B) ≥ P(A) +P(B)−1,
ii) P(A∆B) = P(A) +P(B)−2P(A∩B)

$\displaystyle 1\ge\mathcal{P}(A\cup B)=\mathcal{P}(A)+\mathcal{P}(B)-\mathcal{P}(A\cap B)$
• Oct 11th 2012, 02:05 PM
jennyk
Re: Help with proving probability equations
Thanks but i don't follow/understand this. Maybe i'm hopeless but something more step by step would be great
• Oct 11th 2012, 02:16 PM
Plato
Re: Help with proving probability equations
Quote:

Originally Posted by jennyk
Thanks but i don't follow/understand this. Maybe i'm hopeless but something more step by step would be great

You can't solve $\displaystyle 1\ge a +b-c$ for $\displaystyle c\ge ~?$
If you cannot then you need help at a far deeper level than you can get anywhere online.