Probability of randomly selected person

Question

I would like some help with some problem i saw on a book, Given that there is 80% of a customers has a Salary account on bank (lets call this P(A)), and 50% of the customers have a saving account ( P(b) )?

1. What is the chance of random selected person has both save and salary account?
2. What is the chance of random selected person has save but NO salary account?
3. What is the chance of random selected person has only one type of account ?

Regarding: 1 and 2, im between using the P(A).P(B) OR P(B|A) = P(A).P(B) / P(A)

Answer 1

Assuming $A$ and $B$ are independent,

1. $\mathbb P(A\cap B) = \mathbb P(A)\mathbb P(B)=\frac45\cdot\frac12 = \frac25$.
2. $\mathbb P(B) - \mathbb P(A\cap B) = \frac12 - \frac25 = \frac1{10}$.
3. $\mathbb P(A) + \mathbb P(B) - 2\mathbb P(A\cap B) = \frac45 + \frac12 - 2\cdot\frac25 = \frac12$.