Some blood is found at a crime scene. The police know that it belongs to the one criminal involved. A person’s red blood cells can have type A antigens, type B antigens, both types or neither
type.
In a population:
45% of people have type A antigens but not type B
9% of people have type B antigens but not type A
43% of people have neither type of antigen
3% of people have both types of antigen
An antibody test shows that there are type B antigens present in the red blood cells at the crime scene. What is the probability that the criminal’s red blood cells have both type A and type B antigens?

Answer:

24) D

This is simpler than it looks like (trust me!). There are only 4 different blood groups: A, B, AB and O.

The possibility of the criminal having blood group AB is: 25% (one out of the four possible blood groups).