Answer:
A.It is a binomial variable with mean 17 transformers and standard deviation
transformers.
Step-by-step explanation:
Since the good electrical transformers operate at approximate 85% of the total time and 20 electrical transformers are chosen at random. Assuming the variable is a binomial variable. We have:
Mean = number of samples * probability
Standard Deviation =

mean = 85% * 20 = 0.85*20 = 17 transformers
Standard deviation =
transformers.
Thus, the random variable is a binomial variable.