Answer 1

The probability of a sure event is 1i.e.p(s)=1 where `s` is the sure event . 

Proof: In a sure event n(E) = n(s)

[Since number of elements in Event 'E' will be equal to the number of element in sample-space.] 

By definitions of probability: 

P(s)=n(E)/n(s)=1 

p(s)=1