a. Suppose that every three months, on average, an earth quake occurs is a certain region. Assuming this is a Poisson Process, what is the probability that the next earthquake occurs after three but before seven months?

b. Suppose that, on average,g- particles emitted from a substance follow a Poisson process. Suppose moreover that four particles are emitted every second. What is the probability that will take at least 2 seconds before the next two g-particles are emitted?