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?
Read this: Discrete Random Variables: Mean or Expected Value and Standard Deviation
Standard deviation is square root of variance. And variance is . And is calculated in the same way as E(X).