Of all spam messages, 17.00% contain both the word ‘‘free” and the word ‘‘text” (or ‘‘txt”). For example, ‘‘Congrats!! You are selected to receive a free camera phone, txt ******* to claim your prize.” Of all non-spam messages, 0.06% contain both the word ‘‘free” and the word ‘‘text” (or ‘‘txt”). Given that a message contains both the word ‘‘free” and the word ‘‘text” (or ‘‘txt”), what is the probability that it is spam?

Refer to a large collection of real SMS text messages from participating cellphone users.13 In this collection, 747 of the 5574 total messages (13.40%) are identified as spam.