三个事件的条件概率公式

Question

三个条件概率公式的推导
有事件,a,b,c.已知p(a+b)=p(a)+p(b)-p(ab)则,p(a+b+c)=?

Answer 1

p(a+b+c)=p(a+b)+p(c)-p[(a+b)c]
=p(a)+p(b)-p(ab)+p(c)-p(ac+bc)
=p(a)+p(b)-p(ab)+p(c)-[p(ac)+p(bc)-p(acbc)]
=p(a)+p(b)-p(ab)+p(c)-[p(ac)+p(bc)-p(abc)]
=p(a)+p(b)-p(ab)+p(c)-p(ac)-p(bc)+p(abc)
=p(a)+p(b)+p(c)-p(ab)-p(ac)-p(bc)+p(abc)