Originally Posted by

**MathGeezer** I originally posted this question in the "pre university" section, but got no responses. So, I'm duplicating the post here.

A polygraph test is 90% effective in determining if someone is lying. However, it has a 10% error-rate for "false" detection. A congressman who is known to lie 25% of the time is tested and found to be telling the truth.

A. What is the probability that he could still be lying?

B. If the polygraph test says he is lying, what is the probability that he could actually be telling the truth?