Permutations — Maths STD 11 Science — Question

positive is $\frac{9}{10}$ if the subject has the

serious form, $\frac{6}{10}$ if the subject has the mild form, and $\frac{1}{10}$ if the subject doesn't have the

disease. A subject is tested positive. What is the probability that the subject has serious form of the disease?

1. $\text{P}(\text{A}\cup\text{B})$
2. $\text{P}(\overline{\text{A}}\cap\overline{\text{B}})$
3. $\text{P}(\overline{\text{A}}\cap{\text{B}})$
4. $\text{P}({\text{A}}\cap\overline{\text{B}})$