Probability of a random subset of Z

[Statistics4win]

I'm stuck in this question, could someone give me a hand?

Question 9:
Let $$A = (1,2,3,4)$$ and $$Z = (1,2,3,4,5,6,7,8,9,10)$$, if a subset B of Z is selected by chance calculate the probability of:

a) $$P (B⊂A)$$ B is a proper subset of A
b) $$P (A∩B = Ø)$$ A intersection B =empty set
Appreciate

 

[Evgeny.Makarov]

if a subset $B$ of $Z$ is selected by chance

This may mean different things. What are probabilities of selecting individual subsets if $Z$? If all such probabilities are equal, i.e., if each subset is equally likely, then $P(B\subset A)$ equals the number of proper subsets of $A$ divided by the number of all subsets of $Z$. For the number of subsets see Powerset in Wikipedia. For b) note that $A\cap B=\emptyset\iff B\subseteq Z\setminus A$.