Question

Exercice 3: Rhesus factor, is a type of protein found on the outside of red blood cells. The protein is genetically inherited. A donor is said to have Rh+ blood if the Rhesus factor is present in their blood. Suppose that a blood donation campaign is launched by the University of Ottawa walk-in clinic. Among undergraduate students donating blood to walk-in clinic, 30% have Rh+. 1. If seven undergraduate students donate blood at this clinic on a particular day, what is the probability that at least three of them do not have the Rh factor? What is the probability that the number of students with Rh+ blood will be within 0.1 of the true population mean? 2. How many undergraduate students must donate blood to have the prob- ability of at least one Rh+ donor over 0.90?

Answer 1

1. probty of absent Rh = 0.7, so n=7, p = 0.7 X: no.of ppl w/o Rh, so X ~ Binom(n=7, p=0.7) so P(x > 3) = 0,0.740.37-* = 0.9712 7 k=3 Now, Y ~ Binom(n=7, p=0.3), mean = np = 2.1 so P(2.1 – 0.1 <Y <2.1 +0.1) = P(2<Y < 2.2) = P(Y = 2) = 0.3177 2. Now, we want n s.t. P(Y > 1) > 0.9 P(Y > 1) = 1 - P(Y = 0) = 1-0.7" > 0.9 n>7 so answer = atleast 7