measuring student proficiency

#1
Dear All,
Below is my question;
You are a statistics insctructor and you cover the topic of logistic regression. In order to ensure that your students understand the material , you create a short quiz covering the material from the section.
--Among the students who take the quiz, those who understand logistic regression have an 80% chance of passing the quiz.
--Among the students who take the quiz, those who do not understand logistic regression have a 30% chance of passing the quiz.
--Among the students who take the quiz, 50% pass.

What percentage of the students taking the quiz understand logistic regression?

Any help will be appreciated. Thank you.