Right I will give it a go at explaining the first one, though I am a bit rusty on probability.

1) If you have 2 events A and B there are 4 things that can happen. Just A. Just B. Both A and B. Or even neither! As one of these 4 thingshaveto happen, they must add up to 1.

So P(A)+P(B)+P(A n B)+P(Neither) = 1

Rearranging gives : P(Neither) = 1 - P(A) - P(B) - P(A n B)