Mary is not a nurse. The way to solve this riddle, is to consider statements 4, 5, and 6 and create a chart of all possible true and false answers. Next, fill in the chart according to statements 1 through 3. You will discover that there is only one line where only one of statements one, two and three are true. Thus, it is determined that: Statement 4 and 5 are false and statement 6 is true.