California is hit by approximately 500 earthquakes that are large enough to be felt every year. However, those of destructive magnitude occur on the average once every year. Find the probability that California will experience at least one earthquake of this magnitude during a six-month period. Would it be unusual to have three or more earthquakes of destructive magnitude in a six-month period? Explain, based on the probability of this occurring. (Based on data presented in Earthquake Country by Robert lacopi.)