It's about a diagnostic test,

specificity of 0.90 and sensitivity of 0.98. population prevalence is 1/10 000

Question is what is the prob. that a person who has got two consecutive positive results is ill?

and another one is support you want the prob. of a person being ill after one positive test result to be 0.80, keeping sensitivity and prevalence constant. What is the minimal level of specificity to guarantee that outcome?

Thanks guys!