One way to d esign a spam filter is to look at the words in an email. In particular, some words are more frequent in spam emails. Suppose that we have the following information:

• 50% of emails are spam;
• 1% of spam emails contain the word "refinance";
• 0.001% of non-spam emails contain the word "refinance".

Suppose that an email is checked and found to contain the word "refinance". What is the probability that the email is spam?