Hi i am new to this so can you please help with the following

Let A,B,C be events. Explain why

1. P(AuBuC)= P(A) + P(B/A) + P (C/(AUB)).

Deduce that

2. P(AUBUC)< P(A)+P(B) + P(C)

3. Formulate and prove a version of part (2) for n events.

Thank you