Question

Voltage sags and swells. Refer to the Electrical Engineering (Vol. 95, 2013) study of transformer voltage sags and swells, Exercise 2.76 (p. 86). Recall that for a sample of 103 transformers built for heavy industry, the mean number of sags per week was 353 and the mean number of swells per week was 184. Assume the standard deviation of the sag distribution is 30 sags per week and the standard deviation of the swell distribution is 25 swells per week. Suppose one of the transformers is randomly selected and found to have 400 sags and 100 swells in a week.

a. Find the z-score for the number of sags for this transformer. Interpret this value.

b. Find the z-score for the number of swells for this transformer. Interpret this value.​

Answer 1

Answer:

z = 1.567

94.15 %    = 97 Transformers  having lesser sag

z = -3.36

4 %  = 4 Transformers having lesser Swells

Step-by-step explanation:

z score = (value - mean) / SD

mean number of sags per week was 353

the standard deviation of the sag distribution is 30 sags per week

transformers  randomly selected  found to have 400 sags

z = ( 400 - 353)/30

z = 1.567

94.15 %    = 97 Transformers  having lesser sag

mean number of swells per week was 184

the standard deviation of the swells distribution is 25 swells per week

transformers  randomly selected  found to have 100 swells

z = ( 100 - 184)/25

z = -3.36

4 %  = 4 Transformers having lesser Swells