mean and standard deviation

A new young executive is perplexed at the number of interruptions that occur due to employee relations. She has decided to track the number of interruptions that occur during each hour of her day. Over the last month, she has determined that between 0 and 3 interruptions occur during any given hour of her day. The data is shown below. (10 points)

Number of Interruptions in 1 hour Probability

0 interruption .40

1 interruptions .30

2 interruptions .20

3 interruptions .10

(a) On average, how many interruptions per hour should she expect?

(b) What is the standard deviation of numbers of interruptions per hour?