3. (20 points) Show that the mean of a geometric distribution (幾何分配) with a probability of success p is 1/p.

6. (20 points) Severe thunderstorms have been recorded at a given station over a period of 66 years. During this period, the frequencies of severe thunderstorms observed are as follows:Determine if the annual number of severe thunderstorms follow Poisson distribution with λ=1 thunderstorm per year, at 0.05 significance level.