申論題

4. GuardWare Inc. has installed intrusion-detection devices on the campus of a large university.
The devices are very sensitive and, on any given weekend, each one has a 10% chance of being mistakenly activated when no intruder is present. Assume that the mistaken activations of different devices are independent events.
There are six devices in the Administration building. Assume there will be no intruder in that building next weekend.

(a) If two or more of the six devices in the Administration building are activated during the same weekend, the system automatically signals the police. What is the probability that this system will signal the police next weekend?
Answer=__(K)__. Hint: remember the assumption.