Probability                                                                              

One definition of the probability of an event is the limit to which the relative frequency (no. of successes ÷ no. of trials) tends as the no. of trials tends to infinity. That is;

   (iii)Probability trees can illustrate combined events well: e.g. a bag contains 5 blue balls and 10 red balls. Pick one ball at random, keep it out, and then pick another ball without replacement. What is the probability of one of each colour?