People with type O-negative blood are universal donors whose blood can safely be given to anyone. Only 7.2% of the population has O-negative blood. A mobile blood center is visited by 20 donors in the afternoon. Let X denote the number of universal donors among them.
What is the standard deviation of X?

Question

Quizplus · Accepted Answer

The standard deviation of a binomial distribution is sqrt(np(1-p)), where n is the number of trials and p is the probability of success. In this case, n = 20 and p = 0.072, so the standard deviation is sqrt(20*0.072*0.928) = 1.16.

People with Type O-Negative Blood Are Universal Donors Whose Blood