In a specific state, a major flood takes place once every 5 years on average. If you can suppose floods are independent, and that two floods can't happen simultaneously, find the following:
(a) The probability that a flood happens within the first 10 years.
(b) The probability that a flood happens after the first 6 years.
(c) The expected time until a flood happens, and the standard deviation.
(d) Find the 50th percentile of the time until a flood.