Customers arrive at a checkout counter in a department store at an average of 7 customers per hour. i. Determine the mean and variance of customer’s arrival at a checkout counter in a department...

Customers arrive at a checkout counter in a department store at an average of 7 customers per hour.
i. Determine the mean and variance of customer’s arrival at a checkout counter in
a department store.

ii. Find the probability that at least two customers arrive.

iii. What is the probability between nine to eleven customers arrival at a checkout counter in two hours.