Question

(1 point) Select the correct answer(s) from the choices below. Suppose 20 donors come to a blood drive. Assume that the blood donors are not related in any way, so that we can consider them to be independent. The probability that a donor has type "O' blood is 0.06. What is the probability that two donors have type O blood? A. 0.885 B. 0.225 C. 0.370 D. 0.290

Answer 1

Option B: 0.225

Explanation:

We want that two donors among the 20 to have a type O blood, so first we need to make a combination of 20 choose 2, as these two donors can be any group of 2 people among the total of 20:

C(20,2) = 20!(18!*2!) = 20*19/2 = 190

Then, we need to multiply by the probabilities of each case:

probability of two people being type O: 0.06^2

probability of eighteen people not being type O: (1-0.06)^18 = 0.94^18

So, the final probability is:

P = 190 * 0.06^2 * 0.94^18 = 0.2246 = 0.225

The correct option is B