Standard deviation and probability

The number of customers arriving at customer service of a department store follows a Poisson distribution with a mean of ? =4.0 per time unit. A time unit has 10 minutes. Use X to denote the time between two customer arrivals.The mean (or expected value) of X in minutes isThe standard deviation of X in minutes is If one customer just arrived,the probability that the next customer will arrive within the next 2.50 minutes is closest to If one customer just arrived,the probability that the next customer will not arrive within the next 2.00 minutes is closest to…