Question

Suppose a crime was committed. The victim, Abel, says he did not bleed, but the perpetrator bled. We also know that the perpetrator was someone in our class. The blood at the crime scene is type O. Assuming our class is limited to the 42 people who know their blood type, how many people in our class could be the perpetrator?

Answer 1

The number of people in the class who could be the perpetrator based on blood type evidence is 8.

Step-by-step explanation:

The blood type at the crime scene being type O narrows down the potential suspects. Since Abel, the victim, claims not to have bled, we eliminate individuals with type AB blood as they can only receive type AB blood. Additionally, the perpetrator bled, so individuals with blood types A and B are excluded, as they can only receive A or B blood, respectively.

This leaves only individuals with type O blood as potential perpetrators since they can donate blood to all other blood types (A, B, AB, and O). However, among those with type O blood, we need to account for Abel's statement that he did not bleed. This implies that the perpetrator must also have type O negative blood, as individuals with O positive blood could have donated blood to Abel without causing a reaction, ruling them out as the perpetrator.

Given that approximately 12% of the population has O negative blood, among the 42 people in the class who know their blood type, around 5 individuals might have type O negative blood. Therefore, combining those with type O negative blood and excluding individuals with other blood types, there could be approximately 8 individuals who fit the criteria and could potentially be the perpetrator based on the blood type evidence.