Question

A system may become infected by some spyware through the internet or e-mail. Seventy percent of the time the spyware arrives via the internet, thirty percent of the time via e-mail. If it enters via the internet, the system detects it immediately with probability 0.6. If via e-mail, it is detected with probability 0.8. What percentage of times is this spyware detected

Answer 1

This spyware is detected 66% of times.

Explanation:

We have these following percentages:

Seventy percent of the time the spyware arrives via the internet, and in this case is detected 60% of the time.

Thirty percent of the time the spyware arrives via e-mail, and in this case is detected 80% of the time.

What percentage of times is this spyware detected

0.7*0.6 + 0.3*0.8 = 0.66

This spyware is detected 66% of times.