Question

Use Red Cross data to determine the percentage of the population with an Rh factor that is positive (A, B, AB, or O blood types). Use that value for p. How many students in your class have a positive Rh factor? Is this an unusual amount?

Answer 1

The Red Cross data showing the percentage distribution of population with different blood groups and different Rh factors is given below:

Blood type	Percent of Population
O+	37
O–	6
A+	34
A–	6
B+	10
B–	2
	4
	1
Total	100

 

Therefore the percentage of population with a positive Rh factor can be obtained as follows:

p = 37% + 34% + 10% + 4%

   = 85%

   = 0.85

 

In a class of 40 students, the details of blood group along with Rh factor for all of the students recorded as below:

Blood Group with Rh factor	Blood Group with Rh factor
B-	O+
O+	O+
O-	B+
O+	B-
	B+
B+	O+
B+	A-
	O+
	O+
B+	B-
A+	A-
O-	B-
	O+
A-	A+
B+	B-
O+	B+
O-	A+
	A-
	B+

 

From the above record, we observe that 22 students among the 40 had Rh factor positive.

Using the population percentage p = 0.85, the expected number of students with Rh factor positive can be obtained as follows:

E(X) = n ∙ p

        = 40 ∙ (0.85)

       = 34

Here the observed number 22 is much deviated from expected number 34; therefore, we can say that the class observed possesses an unusual percent of students with Rh factor positive, when compared with the population.