A Local Veterinary Clinic Typically Sees 15% of Its Horses

Multiple Choice

A local veterinary clinic typically sees 15% of its horses presenting with West Nile virus. Last month, 100 horses were admitted and 20 of them had been infected with West Nile virus. The probability of seeing 20 or more horses with West Nile virus was calculated based on a Normal distribution with  = 15 and  = 12.75. Which of the following statements is true?

A) Using the Normal approximation to the binomial distribution is justified, because X = 20 > 10.
B) Using the Normal approximation to the binomial distribution is justified, because n is large and exact calculations are too tedious.
C) Using the Normal approximation to the binomial distribution is justified, because np = 15 and n(1 - p) = 85.
D) All of the answer options are correct.