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 mean of X?

Question

Quizplus · Accepted Answer

The mean of a binomial distribution is given by $n \times p$, where $n$ is the number of trials (in this case, 20 donors) and $p$ is the probability of success on each trial (in this case, the probability of a donor being O-negative, which is 7.2% or 0.072). Thus, the mean of $X$ is $20 \times 0.072 = 1.44$.

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