According to the American Red Cross, 7% of people in the United States have blood type O-negative. What is the probability that, in a simple random sample of 500 people in the United States, fewer than 30 have blood type O-negative?

Approach

Step 1 Verify that this is a binomial experiment.

Step 2 Computing the probability by hand would be very tedious. Verify np(1 - p) ≥ 10. Then we may use the normal distribution to approximate the binomial probability.