Question

The American Red Cross says about 38% of the U.S. population has Type O blood. A blood drive is being held at your school. What is the probability that at least 2 of the first 20 blood donors have Type O blood?

Answer 1

To find the probability that at least 2 of the first 20 blood donors have Type O blood, we can use the complement rule. The complement of at least 2 is 0 or 1. So we can find the probability of 0 or 1 donors having Type O blood and subtract that from 1 to get the probability of at least 2.

Step-by-step explanation:

To find the probability that at least 2 of the first 20 blood donors have Type O blood, we can use the complement rule. The complement of at least 2 is 0 or 1. So we can find the probability of 0 or 1 donors having Type O blood and subtract that from 1 to get the probability of at least 2.

The probability of 0 donors having Type O blood is (1 - 0.38)^20 = 0.000227

The probability of 1 donor having Type O blood is (0.38)*(1-0.38)^19*(20 choose 1) = 0.00263

Therefore, the probability of at least 2 donors having Type O blood is 1 - 0.000227 - 0.00263 = 0.997.