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

Multiple Choice

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?

A) 1.16
B) 1.20
C) 1.34
D) 1.44