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- The English Speaking Traveller (from Pao). Suppose you are visiting a
country in which:
- One out of 10 natives speaks English
- One out of five persons is a tourist
- One out of two tourists speak English.
You meet another person and converse in English. Would you deduce that
they are native? ( Use Bayes rule to compute
the probability that they are native.)
- In a city of a million inhabitants, a murder is committed. You
are accused of the crime, although you are innocent. Some hair
is found at the scene which the genetic fingerprinting expert claims
matches your DNA, although you have never been there. During the
trial, the prosecutor asks this expert,
``what is the possibility of getting this same DNA signal from
someone other than the defendant?'' The expert replies, ``the
probability of getting this DNA signal given that the hair is not
from the defendant's head is one in a million.'' You turn to your
lawyer who makes the motion of a knife across the throat with his
finger. Express the information provided by the expert as a
conditional probability. What is the conditional probability that you
committed the crime, given his evidence? Use Bayes rule to compute
it and get yourself acquitted.
Next: From Probability to Statistics
Up: CS2411 - Study Problems
Previous: Simple Probability Calculus
Jon Shapiro
1999-09-23