Question

Two people have left traces of their own blood at the scene of a crime. A suspect, Sam, is tested and found to have type O blood. The two blood traces are found to be of type O and AB, found in local population with frequencies 60% and 1% respectively. Based on the evidence, what are the odds that Sam was one of the two people whose blood was found at the scene?

Answer 1

0.3

Explanation:

From the evidence, they were two persons on the scene with blood type O and AB. The Probability that blood type O committed the crime is 0.5 = 1/2 which is the same as the probability that blood type AB committed the crime.

Since they are 60% of blood type O in the community, the Odds that Sam whose blood type is O was the one found at the scene is 0.5 * 60% = 0.3

0.5 * (60/100) = 0.3