Blood types: The blood type o negative is called the "universal donor" type, because it is the only blood type that may safely be transfused into any person. Therefore, when someone needs a transfusion in an emergency and their blood type cannot be determined, they are given type $O$ negative blood. For this reason, donors with this blood type are crucial to blood banks. Unfortunately, this blood type is fairly rare; according to the Red Cross, only $5 \%$ of U.S. residents have type 0 negative blood. Assume that a blood bank has recruited 18 donors. Round the answers to at least four decimal places.
Part 1 of 3
(a) What is the probability that two or more of them have type O negative blood?
The probability that two or more of them have type $O$ negative blood is 0.2265 .
- Part: $1 / 3$

Part 2 of 3
(b) What is the probability that fewer than four of them have type $O$ negative blood?

The probability that fewer than four of them have type 0 negative blood is $\square$.

Step 1 ：Given that the blood type O negative is the universal donor type and is crucial to blood banks. However, this blood type is fairly rare with only 5% of U.S. residents having type O negative blood. Assume that a blood bank has recruited 18 donors.

Step 2 ：We are asked to find the probability that two or more of them have type O negative blood. The probability is found to be 0.2265.

Step 3 ：We are also asked to find the probability that fewer than four of them have type O negative blood. To find this, we use the binomial probability formula which is given by \(P = C \times (p^k) \times ((1 - p)^{n - k})\), where \(C\) is the number of combinations of \(n\) items taken \(k\) at a time, \(p\) is the probability of success on each trial, and \(k\) is the number of successes.

Step 4 ：In this case, the number of trials \(n\) is 18 (the number of donors), the probability of success on each trial \(p\) is 0.05 (the probability that a randomly chosen person has type O negative blood).

Step 5 ：We calculate the total probability of fewer than four donors having type O negative blood by summing up the binomial probabilities for \(k = 0, 1, 2, 3\).

Step 6 ：The total probability is found to be 0.9891267763910727.

Step 7 ：Rounding to four decimal places, the final answer is \(\boxed{0.9891}\).