An individual has 3 different email accounts. Most of her messages, in fact 60% come into account #1, whereas 30%come into account #2, and the remaining 10% into account #3. Of the messages into account #1, only 1% are spam, whereas the corresponding percentages for account #2 and #3 are 3% and 5%, respectively. What is the probability that a randomly selected message is spam?

the probability is 0.02 (2%)

Step-by-step explanation:

defining the event S = the message is spam, then the probability is

P (S) = probability that a randomly selected message comes from account #1 * probability that the message is spam given that the message is from account #1 + probability that a randomly selected message comes from account #2 * probability that the message is spam given that the message is from account #2 + probability that a randomly selected message comes from account #3 * probability that the message is spam given that the message is from account #3 = 0.6 * 0.01 + 0.3 * 0.03 + 0.1 * 0.05 = 0.02 (2%)

thus the probability is 0.02 (2%)