# Thread: Help with proving probability equations

1. ## 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 thank you... :

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

2. ## Re: Help with proving probability equations

Originally Posted by jennyk
i) P(A∩B) ≥ P(A) +P(B)−1,
ii) P(A∆B) = P(A) +P(B)−2P(A∩B)
$\displaystyle 1\ge\mathcal{P}(A\cup B)=\mathcal{P}(A)+\mathcal{P}(B)-\mathcal{P}(A\cap B)$

3. ## 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

4. ## Re: Help with proving probability equations

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.