Consider a test for illegal drugs that is 98% accurate. Lets test 3000 poeple, 2900 of whom do not use illegal drugs.

Question

What percent of the total positive tests were false?

What is the chance of a person testing falsely positive twice in a row?

Answer 1

of the 3000, you would expect postives from

2900(.98)+100(.02)

2842+2=2844
percent total false positives: 2/2844 x100

change same person twice?
Pr=(2/100)(1/100)
check my thinking, it is early in the morning.